ANALYSIS: Corker, Flake draw line in the sand in questioning Trump's fitness for office The fact that they aren't alone has implications for Trump's ability to govern.

 -- This is no mere Twitter war.

Sen. Bob Corker, R-Tenn., in choosing to revive and escalate his critique of President Trump, has crossed a critical threshold in questioning the president’s fitness for the office. The fact that Corker is not alone in his party — and that is a fact — has implications for Trump’s ability to govern from here.

Enter Sen. Jeff Flake, R-Ariz., who chose the same day as Corker’s rebuke to shock the political world by announcing he wasn’t running for reelection. He’s retiring because he doesn’t like what it means to be a Republican in the Trump era, and doesn’t like what he sees happening to the country and the presidency.

“We must never meekly accept the daily sundering of our country - the personal attacks, the threats against principles, freedoms, and institutions, the flagrant disregard for truth or decency, the reckless provocations,” Flake declared in a remarkable speech on the Senate floor.

Corker, the chairman of the Senate Foreign Relations Committee, is now on the record saying that Trump is “debasing our nation,” engaging in “constant non-truth telling” and even “kneecapping” public servants in his administration who are trying to avert war.

And Flake has recorded for history – and the consideration of his colleagues – that he finds Trump’s conduct to be “reckless, outrageous, and undignified.”

This is not primarily about policy or even personality at this point. It’s different even from fretting, as Corker did a few weeks ago, that Trump is leading the nation “on the path to World War III.”

This is a senior Republican leader and a one-time advocate for Trump coming close to declaring he is not fit for the presidency.

And it’s another veteran conservative flatly saying that the country cannot accept this presidency as a new “normal.”

Corker didn’t answer direct questions today about whether he believes Trump should be removed from office. But he’s signaling that he regrets his decision to endorse and campaign for Trump, revealing the kind of intraparty schism that may be too deep to ever repair.

“There were many people — I was one of those — who hoped he would rise to the occasion and aspire to lead our nation instead of dividing it,” Corker told reporters today. “He hasn’t risen to the occasion. At this point I realize what we’re dealing with, I think like most Americans.”

Corker, now freed of political considerations, with his impending retirement, claims to be giving voice to concerns shared by some colleagues who are afraid of the repercussions of speaking out.

Flake is now in a similar position. It’s telling – and perhaps chilling – that the senators who are poised to be most forceful in standing up to Trump are also leaving Congress in 14 months.

Corker is playing Trump’s game to some extent. #AlertTheDayCareStaff is quite a hashtag from a sitting United States senator. But he’s also making clear he’s doing so more out of sadness than relishing the moment.

Trump’s responses to Corker, on Twitter, of course, have ignored his wife’s admonishments against name-calling in public life. The president is calling Corker “liddle,” a “lightweight” and “incompetent” and blaming him for President Obama’s Iran nuclear deal and claiming — falsely, according to the senator — that Corker chose retirement only after Trump refused to endorse him for re-election.

From the White House podium today, press secretary Sarah Sanders dismissed the critiques offered by Corker and Flake as “petty comments,” suggesting that the nation would be more successful if Republicans would get in line behind Trump.

Trump is framing the battles as part of his ongoing war with the establishment of both parties. “People like liddle' Bob Corker have set the U.S. way back. Now we move forward!” Trump tweeted today.

But this is different from the Twitter wars that Trump has taken to a form of art. This is not a fight with Rosie O’Donnell or Arnold Schwarzenegger or even with one of the many campaign-season rivals whose physical appearance Trump relished mocking.

Trump today had lunch with senators, with his last best shot at a legislative accomplishment this year on the line. Corker and Flake have revealed concerns that cut far deeper than that, though — with questions about the president’s ability to do the job now in the air on Capitol Hill.

This gets to the heart of governing and what it means to be president. Two senators may be the focus of these feuds, but their words carry meanings that are much more profound.