Published: | Updated:

(Bloomberg Government)—History, demographics and the national mood are pointing to one conclusion about the 2018 congressional races: Democrats are well-positioned to bring one-party government in Washington under Donald Trump’s presidency to a screeching halt.

There’s a confluence of evidence indicating a so-called wave election may be building that would allow Democrats to wrest the House of Representatives from Republican control. A Democratic takeover of the Senate will be harder to achieve.

“We are all very sensitive to the political environment we’re in,” said Oklahoma Representative Tom Cole, who led House Republicans’ campaign arm in 2008. Republicans are girding for an “extraordinarily competitive” election.

Even if only one chamber flips to the Democrats, Trump’s ability to impose his agenda would be thwarted, and his administration almost certainly would find itself pinned down by investigations and subpoenas from congressional committees.

An analysis by Bloomberg Government of historical data, election maps and public polling points to sweeping Democratic gains in the November election, when all 435 House seats and one-third of the Senate are on the ballot.

Since the end of World War II, the party in control of the White House has, on average, had a net loss of 26 House seats in midterm elections. Democrats can win control of the House with a net gain of 24 seats in November. They’d need to win two seats to gain a majority in the Senate.

Adding to that, Trump’s approval rating at this stage of his presidency, 38 percent, is lower than any of his predecessors going back to Harry Truman, according to Gallup polling data. The less popular the president, the more seats his party tends to lose.

Retaking the House in 2018

History and Polling Point To Sweeping Democratic House Gains in 2018

Average result, since 1970, for President’s Party in midterm when job approval is below 50%

33

seat loss

Net gain needed by Democrats to take control of the House

24

seats

History and Polling Point To Sweeping Democratic House Gains in 2018

Average result, since 1970, for President’s Party in midterm when job approval is below 50%

Net gain needed by Democrats to take control of the House

24

33

seat loss

seats

Sources: Gallup, American Presidency Project

That translates to “a very poor chance of bucking the midterm odds if it holds at this level,” Republican pollster Lance Tarrance wrote in a Jan. 5 analysis for Gallup. “Trump’s 20-point approval deficit in recent Gallup polling does not bode well for him, in part because none of the past five presidents saw an increase in their approval rating in the year before their first midterm.”

President’s Midterm Party Losses

History and Polling Point To Sweeping Democratic House Gains in 2018

Presidential job approval at midterm

Midterm election House seats gained or lost by President’s party

Clinton

66

1998

4

G.W. Bush

63

2002

8

Reagan

63

1986

–5

G.H.W. Bush

58

1990

–8

Nixon

58

1970

–12

Ford

54

1974

–48

Carter

49

1978

–15

Clinton

46

1994

–54

Obama

45

2010

–63

Reagan

42

1982

–26

Obama

40

2014

–12

G.W. Bush

38

2006

–30

History and Polling Point To Sweeping Democratic House Gains in 2018

Presidential job approval at midterm

Midterm election House seats gained or lost by President’s party

Clinton

Reagan

Nixon

Carter

Obama

Obama

1998

1986

1970

1978

2010

2014

G.W. Bush

G.H.W. Bush

Ford

Clinton

G.W. Bush

Reagan

2002

1990

1974

1994

1982

2006

66

63

63

58

58

54

49

46

45

42

40

38

8

4

–5

–8

–12

–12

–15

–26

–30

–48

–54

–63

History and Polling Point To Sweeping Democratic House Gains in 2018

Presidential job approval at midterm

Midterm election House seats gained or lost by President’s party

G.H.W. Bush

Ford

Clinton

G.W. Bush

Reagan

Nixon

Carter

Clinton

Obama

Reagan

Obama

G.W. Bush

1998

2002

1986

1990

1970

1974

1978

1994

2010

1982

2014

2006

66

63

63

58

58

54

49

46

45

42

40

38

8

4

–5

–8

–12

–12

–15

–26

–30

–48

–54

–63

Sources: Gallup, American Presidency Project

Republicans do hold some cards. Those include favorable electoral maps drawn by Republican-dominated state governments after the last census. GOP candidates also should be able to run on solid U.S. economic growth, a 26 percent surge in the S&P 500 Index since Trump took office and an unemployment rate that stood at 4.1 percent at the end of the year.

Yet none of the good economic news has budged Trump’s stubbornly low approval ratings so far, or what polls show is a sour public view of the direction of the country.

In that environment, Democratic candidates are swarming to run in Republican-held districts and drawing donors. Through the end of September, 145 House Democratic challengers to 73 Republicans raised at least $100,000, according to the Campaign Finance Institute. At a similar point in 2015, 35 Democratic challengers to 25 incumbent Republicans raised more than $100,000.

Republicans currently hold a 238-to-193 edge in the House, with four vacancies, and a 51-to-49 advantage in the Senate, but there’s a lot of turnover in their ranks. There are 40 House Republicans who’ve announced they’ll retire or leave to run for another office, or have resigned for other reasons. Several of them are in districts won by Hillary Clinton in the 2016 presidential race. Among Democrats the number of departures is 16.

Three Senate Republicans aren’t running for re-election. Two of them, Jeff Flake of Arizona and Bob Corker of Tennessee, publicly split with Trump and likely would have faced significant primary challenges from the party’s right wing, highlighting some of the ideological splintering among Republicans.

Balance of Power

History and Polling Point To Sweeping Democratic House Gains in 2018

Republican

Democrat

Vacant

House membership

193

Democrats

238

Republicans

435 seats

Senate membership

49

Democrats*

51

Republicans

100 seats

History and Polling Point To Sweeping Democratic House Gains in 2018

Republican

Democrat

Vacant

House membership

Senate membership

193

Democrats

238

Republicans

49

Democrats*

51

Republicans

435 seats

100 seats

*Independents Bernie Sanders of Vermont and Angus King of Maine caucus with the Democrats and are shown in blue.

The off-year and special elections conducted since Trump took office underscore the Republican challenges.

Democrats won governors’ offices by wide margins in New Jersey and Virginia while also capturing Republican seats in both states’ legislatures, as suburban voters shifted to Democratic candidates. In Alabama, Doug Jones became the first Democrat elected to the Senate from the state in 25 years in a race that featured a scandal-tarred and controversial Republican who divided his own party, even though he had Trump’s endorsement.

“That’s three pretty big canaries in the coal mine that ought to warn you that you’re headed into a turbulent period in the next election,” Cole said.

Another indicator comes up on March 13 in a special election for a House seat in southwestern Pennsylvania.

Trump won the district by 20 percentage points and Democrats didn’t field a candidate there in the last two elections. But the Republican Party is investing heavily to hang on to it. Trump paid an official visit there on Jan. 18, and both Vice President Mike Pence and House Speaker Paul Ryan are set to help the Republican candidate, Rick Saccone, raise money. If Saccone barely squeaks by, and certainly if Democrat Conor Lamb wins, it would be a shift of momentum that other campaigns will take seriously.

Educated Voters

Democrats improved their showing in well-educated, historically Republican areas in the 2016 and 2017 elections, so some hard-fought races in the fall will be in the suburbs. Among the House districts that may be in play are those of Representatives Rodney Frelinghuysen and Leonard Lance in New Jersey, John Culberson in the Houston area, Barbara Comstock in the Virginia suburbs near Washington, and Peter Roskam in the Chicago area.

“I would not want to be an incumbent Republican member of Congress going into these midterms, especially in a suburban swing community,” said Jesse Ferguson, a former deputy executive director of the Democratic Congressional Campaign Committee, the political arm of House Democrats. “It is a toxic brew of typical midterm rejection of the party in power, combined with a historically unpopular president and a historically unpopular congressional agenda.”

Little public polling is done for individual House races. But one indicator is the generic ballot preference question on national polls that asks voters whether they would prefer a Democratic or Republican candidate in their district. In the average of polls compiled by RealClearPolitics, Democrats have held a steady lead that’s currently at 7.9 percentage points.

Voter Preference for Congress

History and Polling Point To Sweeping Democratic House Gains in 2018

50%

Democrats

46.7%

45

Republicans

40

38.8%

35

April

July

Oct.

Jan.

2017

2018

History and Polling Point To Sweeping Democratic House Gains in 2018

50%

46.7%

Democrats

45

Republicans

40

38.8%

35

April

July

Oct.

Jan.

2017

2018

Source: RealClearPolitics Generic Congressional Ballot Poll average as of Jan. 24

Look for Republican candidates in competitive districts to emphasize local issues and legislative accomplishments for their home areas while also highlighting their independence from Trump, if he remains unpopular.

“You need to have an identity that is different than just being a generic Republican congressman,” Cole said.

Targets for Democrats include the 23 districts that voted in 2016 for Clinton and for a House Republican. Seven are in California. There are another 12 Republican-held districts that Trump won but had voted to re-elect Democratic President Barack Obama in 2012. Seven of those are in New York and New Jersey.

Republicans have far fewer opportunities on offense and will look to offset expected losses by targeting some of the 12 districts that voted for Trump and a House Democrat in 2016.

Some House Seats Parties Hope to Flip in 2018

History and Polling Point To Sweeping Democratic House Gains in 2018

Congressional districts held by

Republican

Republican district carried by Clinton

Democrat

Democratic district carried by Trump

Vacant

History and Polling Point To Sweeping Democratic House Gains in 2018

Congressional districts held by

Republican

Republican district carried by Clinton

Democrat

Democratic district carried by Trump

Vacant

History and Polling Point To Sweeping Democratic House Gains in 2018

Congressional districts held by

Republican

Republican district carried by Clinton

Democrat

Democratic district carried by Trump

Vacant

Sources: U.S. House of Representatives, Bloomberg research

Senate Balance

In the Senate, where one-third of members come up for election every two years, Republicans may cling to their majority only by the good fortune of a friendly map.

Democrats have 26 of their seats on the line in November compared to just eight for Republicans—one of the most politically skewed Senate-election maps in history.

Senate Seats up for Election

History and Polling Point To Sweeping Democratic House Gains in 2018

Republican

Democrat

8

26

2018

12

21

2020

12

22

2022

History and Polling Point To Sweeping Democratic House Gains in 2018

Republican

Democrat

8

12

12

26

21

22

2018

2020

2022

Source: U.S. Senate

Note: The winner of the 2018 Senate special election in Minnesota will finish the six-year term won by ex-Sen. Al Franken (D) in 2014. The winner of that contest will be up for re-election in 2020, therefore 101 seats are shown. Independents Bernie Sanders of Vermont and Angus King of Maine caucus with the Democrats and are shown in blue. Both are running in 2018.

Ten of the 26 Democrats are from states Trump won in 2016. Five are defending seats in states the president won by at least 18 percentage points. They include Senators Joe Manchin in West Virginia, whose Republican opponents include Representative Evan Jenkins and state Attorney General Patrick Morrisey; Claire McCaskill of Missouri, challenged by state Attorney General Josh Hawley; and Indiana’s Joe Donnelly, who likely will face either Luke Messer or Todd Rokita, both House members.

Democrats are seeking to unseat Dean Heller in Nevada, the only state Trump lost in 2016 where a Republican is defending a Senate seat. Democratic Representative Jacky Rosen is opposing Heller, who also faces a primary challenge from Danny Tarkanian, a businessman and frequent candidate.

The Democrats are also making a serious takeover bid in Arizona, where Flake is eschewing a re-election bid in a state Trump won by 3.5 percentage points. The likely Democratic nominee is Representative Kyrsten Sinema.

Democrats face longer odds but have credible candidates in the more heavily Republican states of Texas, where Ted Cruz is seeking a second term, and Tennessee, where Corker is retiring.

Republican Advantages

For all of their challenges, House Republicans can cling to a few mitigating forces that could give them hope of holding off a Democratic wave.

Key among them are structural advantages in the electoral map.

Republicans dominated state-level elections in 2010, giving them the upper hand when congressional districts were redrawn after the last national Census. They concentrated Democratic voters to create overwhelming Democratic majorities in the core of bigger metropolitan areas but with fewer seats. Republican votes, by contrast, are more efficiently distributed over a broader number of congressional districts.

Republican-Friendly Senate Election Map

History and Polling Point To Sweeping Democratic House Gains in 2018

Senate seats up for election, held by

Republican

Republican in state carried by Clinton

Democrat*

Democrat in state carried by Trump

No Senate election

Five Democrats are defending seats in states the president won by at least 18 percentage points

Tester

(Mont.)

Heitkamp

(N.D.)

2

Donnelly

(Ind.)

McCaskill

(Mo.)

Manchin

(W. Va.)

History and Polling Point To Sweeping Democratic House Gains in 2018

Senate seats up for election, currently held by

Republican

Republican in state carried by Clinton

Democrat*

Democrat in state carried by Trump

No Senate election

Five Democrats are defending seats in states the president won by at least 18 percentage points

Jon Tester (Mont.)

Heidi Heitkamp (N.D.)

Joe Manchin (W. Va.)

2 seats

Claire McCaskill (Mo.)

Joe Donnelly (Ind.)

History and Polling Point To Sweeping Democratic House Gains in 2018

Senate seats up for election, currently held by

Republican

Republican in state carried by Clinton

Democrat*

Democrat in state carried by Trump

No Senate election

Five Democrats are defending seats in states the president won by at least 18 percentage points

Joe Donnelly (Ind.)

Jon Tester (Mont.)

Heidi Heitkamp (N.D.)

2 seats

Joe Manchin (W. Va.)

Claire McCaskill (Mo.)

Sources: U.S. Senate, Bloomberg research

*Bernie Sanders of Vermont and Angus King of Maine, both independents running for reelection, caucus with the Democrats and are shown in blue.

Note: Republican Senators in Arizona, Utah and Tennessee are retiring and not seeking reelection

That was illustrated in the presidential election. Although Trump won 2.9 million fewer popular votes than Clinton, he carried more congressional districts, 230 to 205.

And the election is still nine months away. Continued economic growth and the impact of voters seeing more take-home pay as a result of the Republican tax cuts could shift public attitudes toward Trump.

In individual races, the candidates the Democrats run can matter as much as broader national issues, and Republicans can exploit the considerable political advantages of incumbency. Those GOP officeholders are steeling themselves for a turbulent election that won’t take any of them by surprise.

“Open seats are a key part of a potential Democratic House takeover,” Kyle Kondik, the managing editor of Sabato’s Crystal Ball at the University of Virginia’s Center for Politics, said in a Jan. 18 analysis, “but the majority of Democratic gains will have to come from beating GOP incumbents.”

Updates Gallup poll numbers in sixth paragraph and new number on congressional departures in 12th paragraph

Greg Giroux is an elections reporter for Bloomberg Government