By Amber Phillips

When a United States senator, particularly one as powerful and secure as Sen. Bob Corker, R-Tenn., decides not to run for reelection next year, some obvious next questions are: Does his desire to leave have anything to do with Washington? And will others decide to exit, too, potentially changing the balance of power in Washington?

Amber Phillips (Washington Post photo)

The answers aren't entirely clear. When and whether to leave a job is an extremely personal decision. Corker said in his retirement statement that he initially ran for the Senate intent on serving just two terms.

"When I ran for the Senate in 2006, I told people that I couldn't imagine serving for more than two terms. Understandably, as we have gained influence, that decision has become more difficult. But I have always been drawn to the citizen legislator model, and while I realize it is not for everyone, I believe with the kind of service I provide, it is the right one for me."

But it's worth noting the environment that Corker, who chairs the powerful Foreign Relations Committee and was once a Trump foreign policy adviser and potential vice presidential contender, is leaving.

Republicans control Congress for the first time in a decade, but instead of coming together, they've devolved into several factions that have made it nearly impossible to deliver on their central campaign promise for the past seven years.

And Corker's retirement announcement comes on the same day that Senate leaders acknowledged they would not be voting on a last-ditch effort to repeal Obamacare because they didn't have enough votes.

A conservative website editor and Trump confidant has declared war on Republicans in Congress and is considering actively trying to oust key senators. Corker has two nominal primary challengers. His retirement also comes on the same day that a former judge who was kicked off the state Supreme Court could win a Senate race in Alabama, despite the party spending millions against him.

On top of all this, Republicans have a president who doesn't share many of their conservative values, who often distracts from their accomplishments with controversy and who shows little to no interest on policy.

At least one controversy clearly irked Corker.

"The president has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful," Corker told local reporters in August after Trump appeared to equate white supremacist marchers in Charlottesville with counterprotesters.

In short, things aren't going smoothly for Republicans right now. It's entirely possible, even likely, that all of this factored in Corker's decision.

Whatever his reason, his retirement isn't good news for Republicans.

Trump won Tennessee by 26 points in November, so Corker's seat is probably safe, especially since Rep. Marsha Blackburn, R, and Gov. Bill Haslam, R, are rumored to want it. There is a Democratic candidate running there, and Washington Democrats say they're closely monitoring the race. But trying to win an open seat is much more difficult than helping a senator get reelected.

Plus, Corker's retirement could motivate other senators unhappy with the state of affairs to reasses their life choices. GOP strategists told The Post that more retirements are coming, especially in the House.

Already half a dozen House Republicans have retired this year without another job lined up. Several have suggested the party's climate is a big reason why. "It was just a realization that I could keep getting elected, but it's not about getting elected," said Rep. Ileana Ros-Lehtinen, R-Fla., when she announced her retirement in April.

Retirements in the House could put their majority at risk. The Senate, where Republicans hold 52 of 100 seats, is less endangered. But more retirements means more work Republicans have to do to stave off insurgent primary challengers, instead of taking advantage of a very friendly 2018 playing field to pick up more seats.

"There are retirements every year and it's a mistake to read too much into them," said GOP strategist Alex Conant. "But I do hear that more retirements are coming, and at some point it makes maintaining the majorities more challenging."

"Retirement makes it more likely that a far-right candidate wins a GOP primary and, assuming that person wins the general, it makes it more difficult for [Senate Majority Leader Mitch] McConnell, R-Ky., to manage his majority," said Molly Reynolds, a congressional expert at the Brookings Institution.

That's all possible, not probable. But it's much more possible now that a prominent establishment Republican is retiring rather than staying in a divided Congress. Republican leaders, themselves frustrated right now, are surely asking themselves: Will others follow Corker out the door? If so, it's the last thing Republicans need right now.

Amber Phillips writes about politics for The Washington Post. She was previously the one-woman D.C. bureau for the Las Vegas Sun and has reported from Boston and Taiwan.