The announcement by Congressman Darrell Issa on Wednesday that he is retiring brings to 31 the number of open seats held by Republicans in the 2018 midterm elections.

Democrats need to win 25 seats to take control of the House of Representatives.

The unprecedented number of Republican retirements, which includes the sitting chairmen of eight different congressional committees, is a bad omen for the speaker, Paul Ryan, as he seeks to keep control of the lower chamber.

So far, five Republicans representing districts where Hillary Clinton won in 2016 are not seeking re-election this year. Four of them, including Issa, are retiring. The fifth, Martha McSally of Arizona, is seeking the state’s open Senate seat in a competitive primary against Tea Partier Kelli Ward and controversial former sheriff Joe Arpaio.

Issa had the closest race of any member of Congress in 2016. He beat his Democratic opponent Doug Applegate by 1,600 votes in a district that swung heavily against Republicans in the presidential race. Clinton won by seven points in a district that Republican Mitt Romney won by a similar margin in 2012.

Issa’s retirement is a major blow to House Republicans in a district that analysts had considered a toss-up. Not only was Issa a nine-term incumbent but as one of the richest members of Congress, he was able to self-fund his campaign.

His decision not to seek another term makes him the second swing-district California Republican to retire in the past week. On Monday, Ed Royce, the chairman of the House foreign relations committee, announced he too would retire. Royce, a 13-term incumbent, represents a district where Clinton won by nearly 10 points in 2016.

Both California Republicans are victims of the changing political demographics of the state. They both represent parts of Orange County, the once deep-red bastion of suburban conservatism that has undergone a transformation in recent years. In 2016, Clinton became the first Democrat to win there since Franklin Roosevelt in 1936.

However, Republicans see a silver lining in the sheer number of Democratic challengers in some of these races. As the Washington Post reported earlier in January, there are more Republican-held districts with eight Democratic hopefuls than with only one. Republicans hope to take advantage of Democratic infighting to win.

In a statement following Issa’s retirement, Steve Stivers, the head of the National Republican Congressional Committee, said: “In the 49th district, Democrats are locked in what is fast becoming one of the bloodiest primaries in America. While Democrats fight with each other, Republicans will focus on fighting Democrats – and that’s how we plan to win. We look forward to facing whoever limps out of the Democrats’ battle royale: black and blue, and broke.”

In contrast, Democrats saw opportunity in the Golden State’s changing politics. “California Republicans clearly see the writing on the wall and realize that their party and its priorities are toxic to their re-election chances in 2018,” said Drew Godinich, a spokesman for the Democratic Congressional Campaign Committee in a statement.