After two embarrassing weeks, Tennessee Sen. Bob Corker's team confirmed that he would not run for re-election after all. Corker had announced back in September that he would retire, and Rep. Marsha Blackburn quickly emerged as the clear frontrunner in the GOP primary to succeed him. Corker took advantage of his retirement to get into fights with Donald Trump, though he still remained a loyal vote for him. Corker notably called the White House "an adult day care center" and suggested that Trump's recklessness could put the country "on the path to World War III," and Trump fired back by labeling the senator "Liddle Bob Corker."
But tensions between the two reportedly eased, and that seems to have convinced Corker that he could actually run for re-election after all with Trump's support. However, Blackburn made it very clear that she would stay in the race no matter what, and her allies released poll after poll showing her destroying Corker in a hypothetical primary. Corker hoped that if he could grovel his way back into Trump's good graces, he'd be rewarded with an endorsement that could completely rehabilitate his standing with Tennessee Republicans.
However, Politico reports that the White House made it clear to Corker that Trump wouldn't get involved in a primary, and he eventually seems to have gotten the message. Corker's allies also suggested that he'd make a stronger general election opponent against former Gov. Phil Bredesen, but most prominent GOP establishment figures reportedly had no problem with having Blackburn as their nominee.
This whole episode leaves Blackburn in an even stronger position than she was in before. Polls showed Blackburn dominating former Rep. Stephen Fincher in a primary, but Fincher at least had the money to put up a fight. But Fincher dropped out a week ago and said he wanted Corker to run. The only other noteworthy Republican who is running is wealthy ophthalmologist Rolando Toyos, but he had a not-so-noteworthy $17,000 in the bank at the end of December. Tennessee's candidate filing deadline is April 5, but it looks unlikely that anyone will give Blackburn a formidable primary challenge at this point.