In Tennessee, Sen. Bob Corker (R) is retiring this year, and given the Volunteer State’s political leanings, it was generally assumed Corker’s “red” seat would stay that way. In practice, however, it’s a little more complicated than that.

To the disappointment of the Republican establishment, the Republican nominee in this race will be Rep. Marsha Blackburn (R), a right-wing congresswoman who’s earned a reputation as something of an extremist, even by contemporary GOP standards. Democrats, meanwhile, have rallied behind former Gov. Phil Bredesen (D), who’s already won two statewide races in Tennessee.

Corker is formally backing his party’s candidate, but he raised a few eyebrows recently when he praised Bredesen, touted the former governor’s “crossover appeal,” and vowed not to campaign against him during the campaign. Corker added, in reference to Bredesen, that the Tennessee Democrat was “a very good mayor, a very good governor, [and] a very good business person.”

Yesterday, Corker was offered an opportunity to offer comparable praise for his party’s candidate. It didn’t go well.

[CNN’s Dana Bash] attempted to get Corker to explain why anyone ought to vote for Blackburn. Despite his Twitter endorsement, Corker had a little trouble. The best he could do was suggest that a vote for Blackburn could be critical to the GOP retaining control of the Senate and of course, re-electing McConnell as Senate Majority Leader.

The retiring senator, who seemed determined not to mention Blackburn’s name out loud – repeatedly referring to her only as his party’s “nominee” – was told that his support for the congresswoman didn’t sound like “a ringing endorsement.”

If you watch the clip, note that Corker seemed to be at a loss for words for several seconds, before eventually saying, “I’m supporting the nominee. I have worked with the nominee for some time. And I don’t know what else to say.”

In other words, asked to explain why Marsha Blackburn would be a good U.S. senator, the Republican incumbent couldn’t think of a reason – and seemed reluctant to even say her name.

For what it’s worth, Corker’s hesitation may have made for an awkward television interview, but it’s also understandable. As we discussed last fall, a small group of 11 far-right House Republicans unveiled a “birther” bill in Congress in 2009, requiring presidential candidates to prove they’re native-born citizens, and Blackburn was one of the 11.

Blackburn not only rejects climate science, she also declared two years ago that she believes the planet has been cooling for much of the last decade, evidence be damned. She’s also on record arguing against proposals to guarantee pay equity between men and women, because she believes such efforts are “condescending” to women. When railing against Bush-era ceiling-fan regulations, Blackburn went so far as to adopt Martin Niemoller’s “First they came for…” framing.

It doesn’t help that Blackburn has also championed privatizing Social Security and gutting congressional ethics rules.

In 2016, Blackburn also led a bizarre witch hunt against Planned Parenthood (full disclosure: my wife’s employer), which turned into a farcical embarrassment for both her and Congress.

Let’s also not forget that early on in her congressional career, Blackburn invited a neo-Confederate, secessionist, and slavery apologist to give the opening prayer in the U.S. House.

Given all of this, is it really that surprising that Bob Corker is struggling to think of a reason Blackburn belongs in the Senate?