Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.) announced Tuesday he will not run for reelection in 2018, dealing a blow to GOP leaders already dealing with several political landmines.

Corker, the chairman of the Senate Foreign Relations Committee, said he would leave his seat when his term expires at the end of 2018.

He’s the first senator to announce that he will retire. Sen. Orrin Hatch Orrin Grant HatchBottom line Bottom line Senate GOP divided over whether they'd fill Supreme Court vacancy MORE (R-Utah) has yet to decide whether he will run for reelection.

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An aide for Corker confirmed that he told Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellGraham: GOP will confirm Trump's Supreme Court nominee before the election Trump puts Supreme Court fight at center of Ohio rally The Memo: Dems face balancing act on SCOTUS fight MORE (R-Ky.), fellow Tennessee GOP Sen. Lamar Alexander Andrew (Lamar) Lamar AlexanderGraham: GOP will confirm Trump's Supreme Court nominee before the election The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE and President Trump about his decision to retire before his announcement.

Corker didn't hint at what his next steps would be, saying, “I look forward to finding other ways to make a difference in the future.”

Corker’s announcement came hours after Republicans announced they would not hold an eleventh-hour vote on a bill to make good on their years-long pledge to repeal and replace ObamaCare because they could not secure the 50 votes needed to let Vice President Pence break a tie.

It also precedes a competitive GOP primary in Alabama where Sen. Luther Strange Luther Johnson StrangeSessions hits back at Trump days ahead of Alabama Senate runoff The biggest political upsets of the decade State 'certificate of need' laws need to go MORE (R-Ala.), the establishment candidate backed by Senate Republicans, is trailing conservative former state Supreme Court Justice Roy Moore in polls.

A victory by Moore, who is backed by former White House strategist Stephen Bannon, would be seen as a sign that other incumbent Senate Republicans face a real danger of being defeated in primaries.

Breitbart News, where Bannon is now executive chairman, quickly played the news of Corker’s retirement high on its website saying, “establishment Republican dodges 2018 primary fight.”

Corker has been tight lipped for months about whether or not he would run for a third term, and acknowledged he’s been weighing the decision for most of the year.

He sparked the ire of Trump and his allies in August after criticizing the president’s response to violence in Charlottesville, Va.

“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 said.

A poll by The Tennessee Star released in June found that 41 percent of Republican primary voters wanted to reelect Corker, while 42 percent of respondents wanted someone else to run.

But Corker has downplayed the chances that the White House would primary him, and he had a White House meeting with Trump earlier this month. His office didn’t respond to a request for comment, at the time, about if the two discussed 2018 in the sitdown.

“I have no indications whatsoever that the administration would encourage [a primary],” he told reporters earlier this month. “I've had no conversations with Bannon about it, and I don't know that he's actually specifically — I hear sources say that, but I don't think I've ever heard him say that.”

A source close to the pro-Trump Great America PAC told The Hill earlier this month that they would “definitely be interested in a primary” against Corker. And a source told CNN earlier this month that Bannon and his allies were preparing for primary challenges against a slate of GOP senators, including Corker.

Lawmakers in both parties lamented Corker’s decision to retire.

“His leadership on important issues has helped guide our Conference and had a real impact at home and abroad,” McConnell said in a statement.

Democrats, who consider Corker as part of the “governing wing” of the Republican Party, joined in.

“I also hope this is a wake-up call to all of us in the Senate that we need to recommit ourselves to creating an environment where reasonable, thoughtful people of both parties can come together to solve problems,” Sen. Mark Warner Mark Robert WarnerIntelligence chief says Congress will get some in-person election security briefings Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House approves bill to secure internet-connected federal devices against cyber threats MORE (Va.), the top Democrat on the Senate Intelligence Committee, said Tuesday afternoon.

Corker’s retirement is expected to set off a scramble among Republicans to try to succeed him.

Rep. Marsha Blackburn Marsha BlackburnDemocrats smell blood with new DHS whistleblower complaint Hillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections GOP senators unveil new bill to update tech liability protections MORE (R-Tenn.) told The Hill on Tuesday she's considering running for his Senate seat in 2018 and some consider her to be the favorite.

Conservative activist Andy Ogles, who leads the state's arm of Americans for Prosperity, announced a primary challenge to Corker earlier this month.

Former state Rep. Joe Carr (R), who unsuccessfully challenged Alexander in the 2014 primary, had been openly considering a primary challenge, as had state Sen. Mark Green (R).

Rep. Steve Cohen, a Tennessee Democrat, predicted Republican Gov. Bill Haslam would be a top candidate to step into the race to replace Corker.

The Democratic Senatorial Campaign Committee quickly pounced on the announcement, arguing Republican incumbents “see the writing on the wall” and are “terrified to engage in divisive and expensive primaries.”

“Senator Corker’s decision is the latest example of a key theme driving GOP Senate primaries across the country: divided and leaderless, Republican Senate campaigns have nothing to run on but a string of broken promises, and this dynamic will continue to define Republican Senate primaries across the map,” said Lauren Passalacqua, a spokeswoman for the organization.

In Tennessee, Democrats have been impressed with their Senate candidate, Iraq War veteran and attorney James Mackler. But political handicappers rank the state as solidly or safely Republican.

Corker, who first won election in 2006, has a reputation as a dealmaker — particularly on foreign policy.

He negotiated a deal in 2015 to give Congress oversight of the Iran nuclear deal, and got an agreement earlier this year to slap tougher sanctions on Russia, including limiting President Trump’s ability to unilaterally lift penalties against Moscow.

His announcement comes as the Trump administration is dealing with multiple foreign policy challenges, including potentially walking away from the Iran deal and a growing war of words with North Korea.

“I also believe the most important public service I have to offer our country could well occur over the next 15 months, and I want to be able to do that as thoughtfully and independently as I did the first 10 years and nine months of my Senate career,” Corker said.

Scott Wong, Mike Lillis and Ben Kamisar contributed