After two weeks of dormancy, President Donald Trump’s ugly spat with Tennessee senator Bob Corker flared up again Tuesday after Corker insulted the president on the morning news, saying Trump was “unable to rise to the occasion” of his office and that he should “step aside” on tax reform and diplomacy.

“I think the debasement of our nation will be what he’ll be remembered most for, and that’s regretful,” Corker told CNN.

Trump instantly fired back on Twitter with one of his most scorching strings of invective to date, calling Corker a “lightweight” and “incompetent” who “couldn’t get elected dog catcher in Tennessee.”

Bob Corker, who helped President O give us the bad Iran Deal & couldn't get elected dog catcher in Tennessee, is now fighting Tax Cuts....

— Donald J. Trump (@realDonaldTrump)
October 24, 2017

...Corker dropped out of the race in Tennesse when I refused to endorse him, and now is only negative on anything Trump. Look at his record!

— Donald J. Trump (@realDonaldTrump)
October 24, 2017

Isn't it sad that lightweight Senator Bob Corker, who couldn't get re-elected in the Great State of Tennessee, will now fight Tax Cuts plus!

— Donald J. Trump (@realDonaldTrump)
October 24, 2017

Sen. Corker is the incompetent head of the Foreign Relations Committee, & look how poorly the U.S. has done. He doesn't have a clue as.....

— Donald J. Trump (@realDonaldTrump)
October 24, 2017

...the entire World WAS laughing and taking advantage of us. People like liddle' Bob Corker have set the U.S. way back. Now we move forward!

— Donald J. Trump (@realDonaldTrump)
October 24, 2017

Corker responded in kind:

Same untruths from an utterly untruthful president. #AlertTheDaycareStaff

— Senator Bob Corker (@SenBobCorker)
October 24, 2017

The bitter intramural conflict is unique, as most congressional Republicans go out of their way to avoid triggering Trump’s rage and decline to take the bait when he does snap at them.

It was not ever thus: Corker was an early adopter of Trump’s unlikely presidential run, as THE WEEKLY STANDARD noted in an October 10 editorial:

In March 2016, he issued a statement in response to Mitt Romney’s speech critical of Donald Trump. “Here’s my message to the Republican Party leaders,” Corker stated, clearly meaning those not on board with Trump: “Focus more on listening to the American people and less on trying to stifle their voice. What’s happening in the Republican primary is the result of two things: the fecklessness and ineptness of the Washington establishment in failing to address the big issues facing our country and years of anger with the overreach of the Obama administration. And to be candid, I think the American people should be angrier than they are.” … In April 2016, with Trump nearing the delegate total necessary to become the GOP nominee, Corker applauded Trump’s first major campaign speech on foreign policy—praising the candidate for, yes, “challenging the foreign policy establishment.” Corker was “repulsed,” he said, by those who were considering challenging Trump at the convention in July. Not long after, he suggested that Trump’s Republican critics should “chill”—“My sense is when people are out there saying ‘Never this’ or ‘Never that,’ a better place to be is to chill and let the campaign evolve a little bit and see where the candidate ends up.”

While it’s easy to praise Corker for standing up to Trump now that he has nothing to lose by it, our editors point out that Corker hasn’t made a habit of principled stands.

Trump claims, in characteristically theatrical fashion—we can’t say.

What we know is that Corker has never had much time for any sort of principled or ideological disruption in his decade in the Senate. When a conservative took an important stand, Corker was usually somewhere else. His support for social conservatism was lackluster, his interest in budgetary restraint intermittent. His principal achievement as chairman of the Senate Foreign Relations Committee was to give President Obama the specious legal authority he needed to cut a nuclear deal with a state sponsor of terrorism.