Former Tennessee Gov. Bill Haslam announced Wednesday he will sit out the race for Senate this cycle, teeing up a competitive Republican primary in the contest to succeed retiring GOP incumbent Lamar Alexander.

Haslam, 60, described his choice to forgo another bid for public office as “the hardest vocational decision of my life” in a letter published in The Tennessean. 

“While I think serving in the United States Senate would be a great privilege and responsibility, I have come to the conclusion that it is not my calling for the next period of my life,” he wrote. 

Speculation has swirled around Haslam since Alexander announced six months ago that he wouldn’t seek a fourth term, opening up a seat in a state President Donald Trump carried by 26 points in 2016.

[Podcast: Harry Reid in winter, still dabbling in politics]

Tennessee Republicans were waiting on Haslam to make his decision before announcing their plans. Haslam left office earlier this year after two terms as governor.

Republicans reported to be weighing Senate bids include Bill Hagerty, the U.S. ambassador to Japan, a private equity executive and a former member of Haslam’s cabinet. Alexander identified Hagerty, along with Haslam, as an obvious candidate after he announced his retirement, according to The Tennessean.

Hagerty has White House connections: He fundraised for the president’s joint fundraising committee, the Trump Victory Committee, and served on Trump’s presidential transition team. In a Republican primary that will likely be all about loyalty to the president, Hagerty’s connections to the White House could be advantageous. 

Freshman Rep. Mark Green had spoken about wanting to run for Senate in the past, potentially even in a primary against Alexander, but he has now decided against running. 

Trump had nominated Green, a retired Army flight surgeon who wrote a book about treating Saddam Hussein after his capture, to be secretary of the Army in 2017, but he soon withdrew his name from consideration because of past controversial statements. Green likely would have had an easier time running as the Trump candidate against Haslam than against Hagerty. 

Former Rep. Diane Black, who lost the GOP nod for Tennessee governor last year, also said Thursday she won’t seek the Senate seat. 

Nashville orthopedic trauma surgeon Manny Sethi declared his candidacy for the GOP nomination for Senate in June. He is close to former Senate Majority Leader Bill Frist, with whom he edited a book about health policy.

Other Republicans who could run include 8th District Rep. David Kustoff and his predecessor, former Rep. Stephen Fincher. 

“I’ve been approached by folks from all across Tennessee encouraging me to run, and I look forward to continuing to talk to the people about how to best continue serving our great state,” Kustoff said in a statement Thursday. 

Fincher decided not to seek a fourth term to the House in 2016. He briefly ran for Senate in 2017, but dropped out of the race after a few months, urging retiring Sen. Bob Corker to reconsider his decision. Corker didn’t budge, and he was later succeeded by Rep. Marsha Blackburn. Fincher still has $1.7 million in his campaign account. 

Iraq War veteran James Mackler is currently the only Democrat in the race. He briefly ran for Corker’s seat last cycle, before dropping out after former Gov. Phil Bredesen entered the Democratic primary. Bredesen went on to lose to Blackburn by 11 points. Democrats haven’t won a Senate race in Tennessee since Al Gore won a second term in 1990.