Flake announced on the Senate floor that he would not run for re-election next year and would instead dedicate his final months in office to fighting Trump so that his leadership style never becomes "politics as usual".
"I rise today to say: Enough," Flake said, drawing tears from several colleagues.
The struggle for Corker and Flake, over the months ahead, is whether they can provide room for more Republican critics to emerge. The struggle for others is to achieve something for their silence.
Many Republicans have privately complained about Trump in similar fashion as Corker and Flake, but so far very few GOP senators have fallen into public anti-Trump chorus.
They have remained publicly supportive of Trump, for now, to prevent him from declaring them enemies and turning his base against them. They have chosen job security, with the hope that he will support such big initiatives as cutting taxes.
Senate Majority Leader Mitch McConnell sat expressionless throughout Flake's 18-minute excoriation - then thanked his colleague for being "a very fine man" with "high principles" and "a great team player".
About 30 minutes earlier, McConnell sidestepped the "distraction" that Corker had caused with his morning fight with Trump.
"If there's anything that unites Republicans, it's tax reform," the majority leader said.
Trump didn't talk much about tax legislation during his visit to the Hill. He spent the opening 30 minutes of his closed-door remarks simply reiterating what he considers to be the many accomplishments of his first nine months in office. Most of those things were done through executive actions that took no help from Congress, where the broader agenda items on health care and tax cuts remain have stalled.
"He went over all of the items the Administration has been working on, much of which, I agree with him, the Administration hasn't gotten nearly enough credit for, McConnell told reporters after the lunch.
"Mainly he talked about the accomplishments of the first nine months and then tax reform going forward," added Senator Lamar Alexander.
Alexander said he has told Trump that presidents have the ability - if they focus like a laser - to simply "wear down" Congress and get a major piece of legislation passed within the first 15 to 18 months in office.
If they focus, Alexander said.
Trump's morning demonstrated his continued unwillingness to focus on such a critical issue as tax reform.
An obsessive consumer of morning TV, Trump saw the coverage of Corker's criticisms and started firing back over Twitter, calling Corker a "lightweight" who begged for the President's endorsement but "couldn't get elected dogcatcher".
In all, Trump sent five angry tweets, several of which included accusations against Corker that have been proven inaccurate.
Roy Moore's victory and Bob Corker's retirement are fresh indicators of a Senate that's coming apart
CNN then hunted Corker down in the Senate hallways, where he unloaded further on Trump. He said the President was not a role model for children and that Trump would most be remembered for the "debasing of our nation, the constant non-truth telling".
All that was before 10am local time, three hours before lunch started.
These disputes have become so ordinary that some Republicans just laugh them off, the way Senator Thom Tillis did. Tillis purchased a bag of popcorn before the lunch with Trump and posted the picture on social media, treating the event like going to the movies.
Yet Corker's and Flake's actions demonstrated the growing rage among a few prominent Republican lawmakers willing to speak out against what they perceive to be Trump's degradation of the Grand Old Party's traditionally conservative viewpoints.
Add to their cause Senator John McCain, who has grown only more outspoken in his denunciations of Trump since he was diagnosed with terminal brain cancer in July.
Many of the President's supporters dismiss the criticism as the irrelevant perspective of a trio of senators who will likely never again face Republican voters in a primary - and who enjoy basking in the glow of favourable media attention.
Some of these supporters have already suggested that Corker should retire, right now, for his criticism of Trump.
Corker demonstrated that he's willing to absorb the arrows from Trump and others.
And now, Flake can join him and McCain in a full-time effort to confront Trump and allies like Stephen Bannon, the former White House strategist who was trying to defeat Flake.
Is President Trump trying to beat Republican Jeff Flake next year? Flake doesn't care.
Polls had shown Flake was in a lost cause re-election bid, trailing a former state senator by large margins ever since he published Conscience of a Conservative, a declaration of war against Trump's nativist ways.
The book crushed his support among Arizona's conservatives, whose support for Trump's strong stances against illegal immigration runs high. Instead of calibrating his stances to win next year, Flake linked arms with Corker and took up a new fight.
"We have fooled ourselves long enough that a pivot to governing is right around the corner, a return to civility and stability right behind it," he said in his speech. "We know better than that."
When the speeches concluded, Corker was the first to greet Flake, shaking his hand as the two leading Trump critics embraced. Corker reached the same conclusion last month, opting to retire at the end of 2018 rather than run for re-election.
Flake pleaded with his colleagues to join him in denouncing the President, rather than excusing his actions as those of first-time politician.
"Too often we forgive and excuse our failures so we might accommodate them and go right on failing, until the accommodation itself becomes our principle," he said.
