Ryan’s departure leaves 24 Republican-held seats open for the 2018 midterms. Another three Republican senators are also not seeking re-election.

The resignations mark the largest combined number of incumbents from a single party to step down since 1996, when 28 left Congress. It also exceeds the 21 who resigned during the Watergate scandal in 1974.

Many attribute their decision to leave Congress to the hyper-polarized environment, poor approval ratings and difficulties the Trump administration has created for Republicans in re-election campaigns. Republican lawmakers were more likely to resign or retire if Trump was less popular in their district in 2016, according to CNN.

Here’s a list of all the Republican lawmakers who have announced their resignation from Congress, where the GOP currently holds a 51-49 majority in the Senate and a 237-192 majority in the House:

Senate Republicans not seeking re-election

Sen. Bob Corker (R-Tenn.)

After flirting with the idea of a third term, Corker decided against re-election in February. The announcement came after several public feuds with President Trump beginning in May 2017, in which the president tweeted that he advised Corker on his plans to run in 2018.

Strange statement by Bob Corker considering that he is constantly asking me whether or not he should run again in '18. Tennessee not happy!

— Donald J. Trump (@realDonaldTrump) August 25, 2017

One of the wealthiest members of the Senate, Corker was criticized for reversing his opposition to the Republican tax cut plan in December after raising concerns about the federal deficit. He has since called the Trump Administration “fiscally irresponsible” and said the tax bill was “one of the worst votes” he’s made during his tenure.

Sen. Jeff Flake (R-Ariz.)

Senator Jeff Flake said in Oct. 2017 that he would not seek re-election. “Mr. President, I will not be complicit,” he said in a speech on the Senate floor that sharply criticized President Trump. Flake, who has served in the Senate since 2013, has been one of the most outspoken members of the GOP when it comes to the Trump presidency along with fellow Arizona Senator John McCain, who is not expected to run again.

Sen. Orrin Hatch (R- Utah)

Hatch announced in January that he would not run for a third term. The 86-year-old is the longest-sitting member of the Senate. “I’ve always been a fighter,” he said in a statement. “I was an amateur boxer in my youth, and I brought that fighting spirit with me to Washington. But every good fighter knows when to hang up the gloves.” Former Massachusetts governor and Republican presidential candidate Mitt Romney will run for Hatch’s open seat in Utah.

House Republicans not seeking re-election

The midterm elections will include battles for 24 open House seats currently held by Republicans, with six of these races in Texas, three in Pennsylvania, and three in California:

Rep. Darrell Issa (R-Calif.)

Rep. Ileana Ros-Lehtinen (R-Calif.)

Rep. Ed Royce (R-Calif.)

Rep. Tom Rooney (R-Fl.)

Rep. Dennis Ross (R-Fl.)

Rep. Lynn Jenkins (R-Kans)

Rep. Dave Trott (R-Mich.)

Rep. Rodney Frelinghuysen (R-NJ)

Rep. Frank LoBiondo (R-NJ)

Rep. Ryan Costello (R-Penn.)

Rep. Charlie Dent (R-Penn.)

Rep. Patrick Meehan (R-Penn.)

Rep. Bill Shuster (R-Penn.)

Rep. Trey Gowdy (R-SC)

Rep. Jimmy Duncan Jr. (R-Tenn.)

Rep. Joe Barton (R-Texas)

Rep. Gregg Harper (R-Texas)

Rep. Jeb Hensarling (R-Texas)

Rep. Sam Johnson (R-Texas)

Rep. Ted Poe (R-Texas)

Rep. Lamar Smith (R-Texas)

Rep. Dave Reichert (R- Wash.)

Rep. Paul Ryan (R-Wisc.)

Rep. Bob Goodlatte (R-Va.)

House and Senate Republicans who have already resigned

Sen. Thad Cochran (R-Miss.)

The 80-year-old stepped down after four decades in Congress, citing his ongoing health problems. A special election in November will decide who takes his Senate seat.

Rep. Pat Tiberi (R-Ohio)

After serving for 17 years, Tiberi resigned from Congress to take a new position as president of the Ohio Business Roundtable. His seat will be filled after a special election on May 8.

Rep. Trent Franks (R-Ariz.)

Franks resigned from the House in December after it became public that he asked a staffer to bear his child. He had originally planned to serve through Jan. 2018, but announced his immediate resignation amid an investigation by the Ethics Committee into the allegations that the congressman repeatedly offered an aide $5 million to act as his surrogate. Either Republican Debbie Lesko or Democrat Hiral Tipirneni will replace Franks after a special election on April 24.

Rep. Tim Murphy (R-Penn.)

The pro-life congressman said in Oct. 2017 that he would not seek re-election after it was revealed that he had been accused of verbally abusing aides and pressured his mistress to get an abortion. His seat was taken by Democrat Conor Lamb in the special election on March 13.

Rep. Blake Farenthold (R-Texas)

The four-term congressman, currently under investigation for using taxpayer money to settle allegations of sexual harassment and gender discrimination by a staffer, said in December that he would retire at the end of his term. Then on Friday, Farenthold accelerated his plan by announcing his resignation. “While I planned on serving out the remainder of my term in Congress, I know in my heart it’s time for me to move along and look for new ways to serve,” he said in a statement. Texas Governor Greg Abbott will have to decide whether to schedule a special election on November 6 to decide Farenthold’s replacement or call for an emergency election before then to fill the seat.

Rep. Jason Chaffetz (R-Utah)

The House Governmental Oversight Committee Chairman had said he would retire at some point during his term, but resigned abruptly in May 2017. His seat was filled by Republican John Curtis after a special election in November.