Gov Bill Haslam will not run for the U.S. Senate seat held by retiring Sen. Bob Corker, leaving U.S. Rep. Marsha Blackburn as the likely front-runner.

The governor, who is term-limited, made the announcement Thursday in a news release.

“While Crissy and I will always be grateful for all of the encouragement and support to run for the United States Senate, I am announcing today that I will not be a candidate for Senate in 2018," Haslam said in a statement.

"The primary reason is that I want to remain completely focused on my job as governor. I know that being a candidate for the Senate during my last 15 months as governor would be a distraction from the task at hand."

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The Knoxville Republican had the national stature, state popularity, political experience and financial means to make a competitive run for the seat.

In an interview inside his Capitol office, Haslam elaborated on his decision, saying the likelihood of facing a competitive primary election was not a factor.

After Haslam issued his statement, Blackburn announced she will run for Senate.

“If you run as a candidate in today’s world, particularly in a primary in Tennessee, it’s going to be a battleground,” he said. “I was prepared for that.”

Although he said he’d spoken with Blackburn and former Congressman Stephen Fincher in the aftermath of Corker’s retirement announcement, Haslam said the talks were mostly about each person’s timing for a decision.

He said, ultimately, he was not excited enough about the job.

Haslam said that, although his family was probably pleased he opted to stay out of the race, he was encouraged by many Tennesseans and others outside the state to run. He said he received calls from several U.S. Senators, including Majority Leader Mitch McConnell, R-Kentucky. The governor did not elaborate on the calls.

Haslam, who informed Alexander and Corker about his decision Wednesday night, said it was never closer than a “50-50 call” about entering the race.

Haslam said when he first ran for governor, he felt like he was a part-time mayor.

“I realized how much you leave on the table doing that,” Haslam said, adding that he would regret not being able to be fully commit to his last year as governor.

But the governor quickly said he was not committing to being done with public service in the future, even adding he might change his mind about running for the U.S. Senate after becoming a private citizen in 2019.

“I’m certainly not saying I’m never going to run for office again because I love doing this and if I never get a chance to have a public service job again I’ll be sad about that.”

U.S. Sen. Lamar Alexander is up for re-election in 2020 and is undecided about the race.

Haslam said he did not yet know whether he would support anyone in the 2018 race.

“We’ve had the luxury in Tennessee of having people who had influence far beyond just their vote on an issue and they’ve been statesmen and leaders and I would hope we can elect someone else that can do that too,” he said.

Corker, the former mayor of Chattanooga, said on Sept. 26 he would not seek a third term.

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Former Americans for Prosperity-Tennessee leader Andy Ogles has also announced as a Republican candidate for the post. Fincher, who left Congress in 2016, and Nashville surgeon Manny Sethi are considering entering the race.

James Mackler, a Nashville attorney and Army veteran, is the only declared candidate on the Democratic side though others are considering their options.

The primary election is Aug. 2, 2018.

Reach Joel Ebert at jebert@tennessean.com or 615-772-1681 and on Twitter @joelebert29. Reach Dave Boucher at 615-259-8892, 615-259-889 or dboucher@tennessean.com.