Sen. Bob Corker (R-TN) won’t run for another term in office, he announced Tuesday, creating a vacuum at the head of the Senate Foreign Relations Committee and a vacancy for the Senate that’s likely to be hard-fought in the primary and potentially the general election.

“After much thought, consideration and family discussion over the past year, Elizabeth and I have decided that I will leave the United States Senate when my term expires at the end of 2018,” Corker said in a statement Tuesday afternoon.

The decision means one of the Senate’s most interesting members won’t be around Washington much longer. Corker, a two-term senator, has had President Trump’s ear at times (he’d been on Trump’s short list for Secretary of State) and had shown a willingness to harshly criticize the president when he disagreed with him.

Corker led the charge in pushing through new sanctions against Russia this past summer, which Trump had reluctantly signed after huge bipartisan support in Congress.

And he was particularly critical after Trump’s post-Charlottesville comments blaming “both sides.”

“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 declared at the time.

Trump fired back with a tweet saying Corker had repeatedly asked him whether or not to run again — and insinuating he might face a primary fight.

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

Corker drew bipartisan praise upon his announcement.

“Even when he’s been investigating smugglers’ tunnels near the Gaza strip, talking to foreign leaders, or giving advice to President Trump, Bob has never let his feet leave the ground in Tennessee. He says what he thinks, does what he believes is best for Tennesseans, and has helped lead his colleagues on complicated issues involving the federal debt and national security,”Sen. Lamar Alexander (R-TN) said in a statement. “His absence will leave a big hole in the United States Senate, but I know he’s carefully weighed his decision, and I’m looking forward to seeing what he tackles next.”

His Senate Democratic colleagues were just as kind.

“No matter the challenge, you can always count on Senator Corker to bring a reasoned, thoughtful approach, and to make decisions based not on partisanship but on what he believes is in the best interests of the American people. I am sorry to hear of his decision not to run for another term in the Senate,” Sen. Mark Warner (D-VA) said in a statement. “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.”

This is a real loss for the Senate. https://t.co/wdKOU7ikvS — Brian Schatz (@brianschatz) September 26, 2017

Corker’s retirement is likely to trigger a knock-down, drag-out GOP primary to replace him — and potentially an opening for Democrats in the heavily Republican state if the wrong candidate emerges for the GOP.

Corker was already facing a potential challenge from the populist right from former State Rep. Joe Carr (R), an anti-immigration hardliner who lost a 2014 primary challenge to Alexander.

Other potential candidates include Rep. Marsha Blackburn (R-TN), a Trump ally who has $3 million in the bank, Tennessee Gov. Bill Haslam (R), and Tennessee State Sen. Mark Green (R), who Trump had nominated for Army secretary but was forced to withdraw due to controversial remarks he’d made about LGBT people and Muslims.

One intriguing possibility: Former University of Tennessee (and Indianapolis Colts) football star Peyton Manning, who is rumored to be interested in the race. Manning, a Republican, played golf with Trump earlier this year.

The seat is highly likely to remain in GOP hands, barring disaster — Corker narrowly won his seat in a terrible year for the GOP, 2006, and the state has moved hard right in recent years. Trump carried it by 61 percent to 35 percent last fall. But many of the state’s Republicans have a moderate streak, and the wrong GOP nominee could make things interesting and give Democrats hope that Tennessee could be the third seat they need in their pipe-dreams of winning back Senate control, though that would mean holding all 10 Democratic seats in states Trump won last year and winning both Arizona and Nevada.

Nashville attorney and Iraq War veteran James Mackler (D) was already in the race against Corker, and Democratic strategists think he’s a solid potential nominee. Moderate Rep. Jim Cooper (D-TN) is another name who could be an intriguing statewide candidate, as is former Tennessee Gov. Phil Bredesen (D).

Democrats were happy to highlight Corker’s retirement — though they stopped short of promising to fight for the race.

“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,” the Democratic Senatorial Campaign Committee said in a statement.

This post was updated at 6:06 p.m.