- Sen. Bob Corker is reportedly reconsidering his retirement as some Republicans in his state worry about the GOP's ability to hold his seat.
- As of now, the race will likely feature Republican Rep. Marsha Blackburn and Democratic former Gov. Phil Bredesen.
- Blackburn's campaign says concerns about the congresswoman's ability to win are driven by sexism.
- Tennessee has been a safe state for Republicans, but Democrats see opportunity after winning a Senate seat in Alabama.
Later a spokeswoman for Corker told NBC News the senator is "listening closely" to those who are encouraging him to reevaluate his decision to retire.
Some members of the GOP in Corker's home state want him to run again in this year's midterm elections, according to Politico. The 65-year-old Tennessee Republican, a frequent critic of President Donald Trump, announced plans in September to retire after his current term ends.
Despite their clashes after Corker publicly worried about Trump's competence, the president reportedly wanted him to run for Senate again.
In Corker's absence, the race will likely pit Republican Rep. Marsha Blackburn against Democratic former Gov. Phil Bredesen. While the state has proven reliably Republican in recent elections, Democrats see opportunity in places where they were not previously competitive after Sen. Doug Jones won the Alabama special election last year. The current minority party is trying to win control of the chamber despite a daunting re-election map.
One recent Tennessee poll that overweighted Republicans showed Bredesen with a 2-point advantage, Politico reported. Widely followed sites that rate congressional elections show mixed signals for the GOP: The Cook Political Report rates the race as a toss-up, while Sabato's Crystal Ball rates it as "likely" Republican.
Blackburn's campaign is confident in her ability to win, and the congresswoman has no plans to step aside if Corker re-enters the race. Campaign spokeswoman Andrea Bozek told CNBC that "anyone who thinks Marsha Blackburn can't win a general election is just a plain sexist pig."
"We aren't worried about any ego driven, tired old men," she said, noting that some polls have shown Blackburn with a comfortable lead.
The congresswoman raised about $2 million in the fourth quarter and had more than $4.5 million on hand at the end of the year. She has so far outraised all candidates in the Senate race, including Republican Stephen Fincher and Breseden.
Republicans currently hold 51 seats in the Senate. The GOP's odds of losing control of the chamber appear slim at this point: Democrats have to defend 26 seats in this year's elections, versus only eight for Republicans.
Several Democrats face re-election in states Trump won in 2016 including North Dakota, Missouri, West Virginia, Indiana, Pennsylvania and Ohio.
— NBC News contributed to this report.