Days away from a closely contested election to determine Tennessee's next U.S. senator, two of the state's top Republicans declined to say by name who they are voting for this year.

Republican Marsha Blackburn and Democrat Phil Bredesen are campaigning for the Senate in what has become the most expensive race in state history.

Blackburn, a Williamson County congressman, and Bredesen, a former Tennessee governor, are vying to succeed Republican Sen. Bob Corker.

Corker, who did not seek a third term, told reporters in Nashville on Wednesday that he planned to vote early on Thursday in his home city of Chattanooga. He declined to say specifically how he planned to vote.

Latest polling:Emerson poll shows Blackburn up by 8 points over Bredesen; new CNN poll gives her 4-point edge

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"I think you know, so, I’ll leave it at that," Corker said, at one point looking down at the floor as he answered.

When pressed on whether he meant he would vote for Blackburn, Corker pointed to his endorsement of her this spring, though one that was rather tepid. Corker also has appeared with Blackburn at events over the course of the campaign and his political action committee, Rock City PAC, donated to her.

"Yeah, I endorsed her early on," Corker said.

On Thursday, Haslam also declined to tell reporters specifically how he cast his ballot when he voted early last week.

"I'm obviously a Republican, and I've voted Republican all my life," Haslam said. "I've tried to just stay out of this, because I do think people need to protect, you know, the privacy of the voting box, but it's pretty clear that I vote Republican."

Haslam has offered his praise of Blackburn. He has appeared with Blackburn on the campaign trail, joined her during an Aug. 2 primary event and at a Republican Party unity rally after she won the GOP nomination. Haslam's father, Jim Haslam II, is the Blackburn campaign finance chairman.

Haslam endorsed Republican gubernatorial nominee Bill Lee shortly after Lee won the GOP primary. He called Lee "the right choice to take Tennessee to the next level," in an ad purchased by the Republican Governors Association, which he currently leads.

Haslam has been asked about his voting in the past. The governor came under criticism from some Republicans in 2016 for not supporting Donald Trump for president and said before the election that he wouldn't be voting for him in November 2016.

Corker pledged not to campaign against Bredesen

Corker said earlier this year that while he had endorsed Blackburn as his party's nominee for the seat, he would not campaign against Bredesen, a friend of his.

Bredesen, who served as governor from 2003 to 2011, has campaigned as a centrist, touting his moderate views and willingness to work with Republicans and support President Donald Trump when he agrees with the president's policies.

Blackburn has presented herself as a loyal supporter of Trump, who has campaigned for her in the state on multiple occasions this election. Trump plans another rally for Blackburn on Sunday in Chattanooga.

Corker at times has been outspoken in his criticism of Trump, calling out his party for their "cult-like" support of the president.

When asked after his endorsement of Blackburn why she was the better candidate to replace him in the Senate, Corker said she would help preserve Republicans' control of the chamber and would vote to keep Sen. Mitch McConnell as majority leader.

Reach Natalie Allison at nallison@tennessean.com. Follow her on Twitter @natalie_allison.