Outgoing Sen. Bob Corker, R-Tenn., will not campaign against the Democrat running to replace him this year.

The senator called Democratic former Tennessee Gov. Phil Bredesen a "friend" with whom he has worked for more than 20 years. Corker said Wednesday he does not plan to attack Bredesen, who aims to upset the leading Republican, Rep. Marsha Blackburn, in the red state.

"I'm not going to campaign against someone who I've been a friend with and worked with, you know? So that's the way it's going to be," Corker said at a Christian Science Monitor breakfast. Corker has declined to run for a third Senate term in November.

Despite the challenges Bredesen faces in a state President Donald Trump won with more than 60 percent of the vote, Corker told reporters he thinks the former governor has about a 6 percentage point advantage in the race right now. The winner of the seat will help to determine whether Republicans hold or expand their narrow 51-seat majority in the Senate.

Corker also told the audience that "any Republican senator who hasn't been conflicted over this presidency is either comatose or is pretty useless in their blindness."

Democrats face a daunting task in trying to take the Senate. The party's senators and independents who caucus with them will defend 26 seats in November, including 10 in states Trump carried in 2016. Republicans only face re-election in nine states.

A competitive Tennessee race could change the calculus for the parties. Democrat Doug Jones' special election win in deep-red Alabama last year not only narrowed the GOP majority in the upper chamber but also gave Democrats hopes about competing in more challenging states this year.

Corker has shown some support for Blackburn, who has served in Congress since 2003 and pledged to back Trump's agenda. On Wednesday, he said he sent her campaign a contribution check for an undisclosed amount of money, adding that he is "supportive." However, he said he never had the close working relationship with Blackburn that he did with Bredesen.

Corker said he worked closely with Bredesen when the senator served as mayor of Chattanooga and Bredesen was governor.

Bredesen, 74, is seen as having potential appeal across the state because he served two terms as governor. He won a 2006 re-election bid with nearly 70 percent of the vote.

Bredesen has had to tread carefully in the red state. He has tried to avoid GOP efforts to tie him to Washington's Democratic leaders. He also said in a campaign ad that he is "not running against Donald Trump."

Bredesen thinks taking back the Senate will be daunting for Democrats, even if he wins.

"I don't think it's possible. I'll be honest with you. My expectation is that I will be in the minority in the Senate," he told The New York Times.