Sen. Bob Corker, R-Tenn., announced Tuesday he will not seek re-election to his seat in 2018, making him the first Republican senator to announce his retirement from the Senate ahead of the midterm elections.

A two-term senator and the former mayor of Chattanooga, Corker made the announcement in a statement Tuesday afternoon. He said that while he never imagined he'd stick around for more than 12 years in the Senate, the decision became more difficult due to the considerable influence he has accrued, particularly as chairman of the powerful Senate Foreign Relations Committee.

"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 the statement. "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."

"Serving the people of Tennessee in this capacity has been the greatest privilege of my life. And as I spent the month of August traveling across our great state, I was reminded that we live in a unique place full of people who care deeply about the direction of our country," Corker said.

"I am grateful to the people of Tennessee for the opportunity to serve my state and country. I have been fortunate to do so with an extraordinary staff, and I want to thank them for their incredible dedication. I know that we will continue to have an impact for the remainder of our term, and I look forward to finding other ways to make a difference in the future."

Corker was thought to be one of the incumbents being targeted by the likes of Steve Bannon, the former White House chief strategist and current Breitbart News chairman, and conservatives,. Bannon is also reportedly looking to oust Sens. Jeff Flake, R-Ariz., Dean Heller, R-Nev., and Roger Wicker, R-Miss.

However, the incumbent Republican shot down that chatter after reports emerged he might not seek re-election in early September, saying he had a good relationship with the White House and didn't think Bannon was going to go after him.

"I've always expected that if I run, that I'll have a primary. I have no indications whatsoever that the administration would encourage that ... We see no evidence of it," Corker told reporters on Sept. 11. "I have no reason to believe the administration would encourage a primary. None," he added, repeating the line multiple times.

According to one Tennessee Republican source, Corker's was burned out and thought it was the right time to leave.

"He was burned out and didn't really want to do it anymore," the source said.

As for who could replace the incumbent Republican, Rep. Marsha Blackburn is thought to be the favorite if she seeks the GOP nomination. Blackburn told reporters at the Capitol that she'll look at the possibility.

"I don't know. We'll see," Blackburn said, adding she heard the news about Corker on the House floor during votes.

"He's such a wonderful man," Blackburn said. "I'm know he's going to be missed."

Rep. Scott DesJarlais, R-Tenn., said Blackburn would be a "formidable" opponent if she decides to make the jump towards a 2018 contest.

"I think she's well-known in Tennessee. I think she's been a strong conservative voice, and a thoughtful person that's always been supportive of the president," DesJarlais told reporters. "I think she'd be formidable."

Rep. Diane Black, R-Tenn., also shot down rumors that she could seek the seat and forego her current campaign for the Tennessee governorship. A spokesman told the Washington Examiner that she is "100 percent committed" to her gubernatorial campaign.

"Diane Black remains 100% committed to her campaign for Governor to make Tennessee and even better place to live,work and raise a family," said spokesman Lance Frizzell in a statement.

DesJarlais said that he does not expect to see outgoing Gov. Bill Haslem seek the seat.

"I don't get the impression that that was on his radar, but nothing surprises me," he said

"I hadn't really thought that much about [who could replace Corker.] Of course, a Senate seat opens all kinds of possibilities. So there could be non-political business people that could step up," DesJarlais said. "I don't know if anyone in the governor's race might switch over."

Corker is also known on Capitol Hill as a moderate voice and a member willing to reach across the aisle and work with Democrats to pass legislation. While he is the first centrist Republican senator to announce his departure, a group of House members, including Rep. Charlie Dent, R-Pa., already announced their decision to leave the House after their current term expires amid frustrations in passing legislation.

Senate Minority Leader Chuck Schumer, D-N.Y., lamented the news that Corker will be leaving the upper chamber.

"Bob Corker is a friend and a fine, conscientious, and hard-working senator. His thoughtfulness and dedication to the job make him a model Senator," Schumer said in a statement. "We all regret him leaving."

The decision also means that he will relinquish his chairmanship atop the Foreign Relations Committee. Corker has held the post since 2015 and indicated that the position would be a main reason to seek reelection.

David M. Drucker and Diana Stancy Correll contributed to this story.