The Republican Party’s tenuous grip on the House majority slipped Wednesday after Rep. Darrell Issa became the second California Republican this week to opt for retirement over fighting an uncertain battle for re-election.

Issa, from northern San Diego County, joined retiring Rep. Ed Royce, from historically Republican Orange County, putting two seats targeted by the Democrats further in play as they seek to erase the GOP’s 24-seat House majority.

[FULL LIST: Republicans not running for re-election in 2018]

Their departures raise the number of Republican retirements to 31, a figure not approached since 28 Democrats rushed for the exits in 1994, the year the GOP won control of Congress for the first time in four decades.

The development, coming on the heels of the passage of a major overhaul of the federal tax code, reveals a Republican majority far more nervous about its 2018 prospects than suggested by members’ rosy midterm prognostications.

“We’re actually going to have to be good on our game,” Rep. Pete Sessions, R-Texas, the House Rules Committee chairman, said. Sessions knows an electoral wave; he led the National Republican Congressional Committee, the House campaign arm, in 2010, when the GOP flipped 63 Democratic seats in President Barack Obama’s first midterm.

Republican leaders blame the retirements on internal House GOP rules that term-limit committee chairmanships to six years (three two-year terms.) Several retirees are set to lose their gavels next year, without any guarantee of a high-profile spot to land or future leadership role on another committee, including Royce (Issa lost his a couple of years ago.)

Top Republicans also dispute the “doom and gloom” picture of the election cycle painted by the Democrats and the political press.

In California’s 37th and 49th congressional districts, Democratic presidential nominee Hillary Clinton defeated President Trump by 8.5 and 7.5 percentage points, respectively. Recent national generic-ballot polling showed voters prefer Democrats were in control of Congress by double digits.

But Republicans claim that their internal polling revealed the party trails by just 1 percentage point — a virtual tie. And a party on the ropes doesn’t easily recruit eager, top-tier female candidates to run in the acknowledged tough seats deserted by Issa and Royce, as GOP officials claim to have done.

“We have a term-limited system that the Democrats don’t have and so it results in some chairmen that, when their six years are up, they tend to leave, and that opens up some seats,” said Rep. Steve Stivers of Ohio, the NRCC chairman. “We clearly have to defy history, but I feel comfortable that we’re going to do it.”

Issa told reporters the political environment had nothing to do with his retirement, even though he barely won re-election in 2016. "It was time. I'm going to be 65 and happily looking forward to doing other things," he said.

Republicans control Congress and the White House, opening them up to the midterm backlash that historically afflicts the president’s party. But Trump’s job approval ratings, which generally hover around 40 percent, and his polarizing leadership are driving Democratic enthusiasm, putting the GOP in further danger.

Not all retirements jeopardize seats. Some Republicans are vacating safely drawn districts the Democrats won’t contend for. But the exodus is akin to the party’s major investors selling their stock now, fearing bigger losses on Election Day and worse: entering 2019 in the minority.

About a half-dozen Republicans are abandoning obviously competitive seats; another half-dozen more are leaving to run for higher office. Others are simply calling it quits after years, or decades, in Washington.

Excuses that it has little to do with the challenging political environment are plausible.

But Republicans, in full control of government, and with the Senate’s electoral map favoring the GOP, should be excited to stick around to see what they might accomplish with that power for another two years, until Trump goes before the voters in 2020.

“Nobody wants to be here,” a Republican strategist said.