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WASHINGTON — A growing number of House Republicans are choosing to voluntarily drain the swamp one year ahead of the midterm elections.

Nearly two dozen congressional Republicans have so far announced they will not be running for re-election, leaving Democrats enthusiastic about the potential for major gains in the 2018 elections. Nine Republicans are running for a different elected position, while 12 are retiring.

And while Congressional retirements are common (on average, 22 House members retire each cycle, according to a CQ Roll Call analysis), the numbers so far are glaringly one-sided. Just two Democratic House members have announced retirements, while six are running for a different office.

Five of the departing congressional Republicans hold seats in very competitive districts where President Donald Trump won by seven points or less in 2016. One, Washington Rep. Dave Reichert, represents a district Clinton won.

The wave of GOP departures comes as the party continues to struggle with how to deal with the president, whose popularity hit the lowest point of his presidency in an NBC News/Wall Street Journal poll released late last month. And as Trump ally Steve Bannon is encouraging primary challenges to incumbents he feels are not supportive of the president and his agenda.

Primary threats have already contributed to two GOP senators, Jeff Flake of Arizona and Bob Corker of Tennessee, choosing not to seek re-election.

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"Trump is so polarizing, Republicans have one-third of their voters who want you to denounce him and one-third who want you to defend him," said Republican strategist Terry Sullivan, who ran Sen. Marco Rubio's presidential campaign. "So members are frustrated from the standpoint that they just don't understand voters."

More announcements are likely to be made in the coming weeks, and the complete breadth of retirements will not be clear until the end of the year, according to David Wasserman, House editor for The Cook Political Report.

“Trump and the current political climate are a big reason we’re seeing these retirements. But Trump isn’t the entire reason,” Wasserman said.

The growing extremism in politics, which began well before Trump, is another reason many outgoing Republicans are citing for why they are opting out of life on Capitol Hill.

“Regrettably, our nation is now consumed by increasing political polarization; there is no longer middle ground to honestly debate issues and put forward solutions,” Rep. Frank LoBiondo, R-N.J., said in the statement announcing that he will not seek re-election.

“I've fought to fulfill the basic functions of government, like keeping the lights on and preventing default,” Rep. Charlie Dent, R-Pa., said in his retirement announcement. “Regrettably, that has not been easy given the disruptive outside influences that profit from increased polarization and ideological rigidity that leads to dysfunction, disorder and chaos.”

Rep. Charlie Dent (L), R-Pa., a key moderate in the health care bill debate, explains why he would be voting "no" on the Obamacare replacement on March 23, 2017 while on Capitol Hill in Washington. J. Scott Applewhite / AP file

Republicans currently hold a 239-194 majority in the House with two vacancies, and Democrats would need to pick up a hefty but not impossible 24 seats to regain the majority. The minority party is hopeful that signs of a major wave are there. The NBC News/WSJ poll found 48 percent of voters say they prefer a Democratic-controlled Congress, compared to 41 percent of respondents who say they prefer a GOP majority. The Democrats' advantage is up from September but still lower than the double digit numbers during the 2006 and 2008 cycles, when the party picked up 31 and 21 seats, respectively.

Democrats received further encouraging news Tuesday when they easily won gubernatorial races in Virginia and New Jersey and made major gains in Virginia’s House of Delegates.

“Tuesday’s results should scare the crap out of every Republican in a competitive district,” Sullivan said.

The Democratic Congressional Campaign Committee on Thursday released its “One Year Out” strategy, announcing they plan to target 91 Republican held congressional districts. The memo notes that the retirement trend is likely to continue, calling it “a great deal of advantage for House Democratic challengers.”

Republicans involved in the House re-election efforts note that the number of retirees is still below the historical average and contend that most of the outgoing members are in strongly Republican-held districts.

“We already have a host of quality Republican candidates declared in many of these seats and we’re confident they’ll remain in our column,” said Jesse Hunt, a spokesman for the National Republican Congressional Committee.