More House seats are open in 2018 than in at least a dozen years, but it's no slam dunk for Democrats

• More House seats will not have an incumbent running in the 2018 midterm elections than in any election year since at least 2006.
• The departures skew heavily Republican, with members of Congress retiring or seeking other offices.
• However, it's not clear whether a high number of departures will have any profound effect on November's elections.

Bill Clark | CQ Roll Call | Getty Images

Rep. Paul Ryan

House members are leaving their seats at a rate not seen in at least a dozen years. Yet it remains to be seen how the exodus — particularly on the Republican side — will affect November's fight for control of the chamber.

The most high-profile departure came earlier this month when House Speaker Paul Ryan said he would not seek re-election as he tries to spend more time with his family.

GOP incumbents will not run in 39 districts: 26 in which the member of Congress is retiring and 13 in which the representative is seeking a different office, according to data compiled by Daily Kos Elections. Nineteen Democratic seats will be open due to retirements, campaigns for another office and one death.

The current total of 58 open seats has already topped every election cycle dating back to 2006, according to the Daily Kos data. Tough electoral dynamics for some Republicans and term limits on committee chairmanships have contributed to the high number of departures.

Due to a loss of name recognition or fundraising strength, defending House seats becomes more difficult without an incumbent. However, recent elections suggest the increase in departures may not necessarily lead to a strong 2018 performance for the Democratic Party as it tries to flip the 23 GOP-held seats needed to take a House majority.

The president's party often struggles in midterm elections, and President Donald Trump's sluggish approval rating and energetic opposition to his policies may hurt GOP candidates. Those factors may play a bigger role in the 2018 results than retirements, said Steven Billet, director of the legislative affairs program at George Washington University's Graduate School of Political Management.

Retirements "allow the other party to be a bit more hopeful" about their prospects, he said. But he cautioned against using retirements to draw conclusions about November's outcome.

"Obviously, Donald Trump is playing a role here, retirements are playing a role here, the presidential party losing seats in off-year elections is playing a role," he said.

The number of GOP retirements suggests Republicans think the electoral environment will be difficult for them in November, said Molly Reynolds, a fellow in governance studies at the Brookings Institution. However, she also said it is tough to assess how departures will affect the midterm results.

"It's difficult to figure out just how big a role the retirement itself plays in determining the outcome, since members who think they might lose are more likely to decide not to run," Reynolds said.

Currently, Democrats have about a 6 percentage point lead in an average of recent polls asking which party voters would prefer in the midterms, according to FiveThirtyEight. That gap has narrowed from about 10 percentage points in January.

Recent results show no clear trend for House departures alone affecting election outcomes. In 2010, more Republicans left office than Democrats, yet the GOP gained 63 seats and control of the House. It was the first off-year election held during President Barack Obama's tenure, in which energized opposition to the Affordable Care Act propelled the GOP.

In 2012, more Democrats departed than Republicans. Democrats picked up a few House seats but failed to gain control of the chamber. Obama won re-election that year.

Then, in 2014 — another midterm year in which more Republicans left office than Democrats — the GOP again gained seats and kept control of the House.

This year, races for GOP-held seats without incumbents vary in how competitive they appear. Republicans seem safe in several seats incumbents left, such as Indiana's 6th District, Mississippi's 3rd District, South Carolina's 4th District and at-large seats in both North Dakota and South Dakota.

But other GOP members of Congress are choosing not to run again in areas considered particularly vulnerable for the party. Those seats include Florida's 27th District and Pennsylvania's newly redrawn 5th, 6th and 7th Districts.