On Tuesday, Sen. Jeff Flake (R-Ariz.) took to the floor of the Senate and did something Americans rarely see — he delivered a stirring jeremiad against a sitting president of his own party.

"Reckless, outrageous, and undignified behavior has become excused and countenanced as 'telling it like it is,' when it is actually just reckless, outrageous, and undignified," Flake said, in an unmistakable criticism of President Donald Trump. "And when such behavior emanates from the top of our government, it is something else: It is dangerous to a democracy."

It was a stunning repudiation of the president, made all the more powerful by the fact that another Republican senator, Bob Corker, had spent recent days delivering his own blistering critique of Trump in the media. And when all was said and done, the response from the anti-Trump left — or some quarters of it, anyway — was clear:

Not. Good. Enough.

"Where [were] their spines all throughout 2016?" grumbled one. "Jeff Flake is not a hero, despite what he wants you to think," thundered ThinkProgress. "Jeff Flake and Bob Corker are cowards," declared my colleague David Faris.

All of which raises the question: Can the anti-Trump left take "yes" for an answer?

Liberals have long regarded Trump as a unique threat to American institutions, civil rights, and democracy. Since he took office in January, it has been clear to most observers that effectively resisting and containing his presidency will require something unusual — the willingness of leading Republicans to cross party lines.

Part of the reason for this is math: Republicans control the White House, Congress, the Supreme Court, and most state governments. Democrats simply don't have the political power to stop Trump — or even slow him much — on their own. But Republicans do have the power to stymie Trump. Remember, the failure of congressional Republicans to repeal ObamaCare ultimately came down to a few GOP defectors in the Senate.

Another reason why the anti-Trump left needs Republicans: Legitimacy. Nobody cares if Democrats oppose a Republican president, or vice versa. That's just politics. But the public takes opposition more seriously when members of the president's own party are involved. In 1974, it took a contingent of Republicans led by Sen. Barry Goldwater — like Flake, an Arizona Republican — to convince Richard Nixon that it was time to resign.

Resistance, it seems, requires bipartisanship.

You wouldn't know that, however, from the liberal response to the growing number of Republicans speaking out against Trump.

Bob Corker says the president needs "daycare." Not good enough. John McCain speaks out against "spurious nationalism." Not good enough. George W. Bush declares his opposition to "bullying and prejudice in our public life." Not good enough. "The differences between Bush and Trump are superficial," sniffed The New Republic's Jeet Heer.

This is nonsense. The problems with Trump go way beyond policy. Yes, Republicans like Corker, Flake, McCain, and Bush probably share some policy stances (especially on taxes) with Trump. No surprise: They're all Republicans. It's also true that Trump's policies, to the extent that he has coherent policy views, are bad for the country. But that wouldn't be enough to arouse Trump's own party against him.

The larger problem — one that has nothing to do with ideology — is temperament. Trump is self-evidently a narcissist, capricious, and bullying. The evidence is that his own staff treats him like a toddler, limiting the information he receives and flattering him endlessly, all to curb his worst excesses.

This is what transforms Trump from merely an awful president to a dangerous one. George W. Bush, for all his many faults, didn't keep us up at night wondering if nuclear war was in the offing. Republicans and Democrats don't need to agree on anything else if they agree that Trump's character makes him unsuitable for office.

Remember, too, that joining the opposition is a process. Liberals seem to want their allies fully formed, fully woke, and fully on board the anti-Trump bandwagon from Day One. It points to a larger problem in our politics: Folks on both sides have decided we don't need to try and persuade people who aren't already on our side — we don't even really want to.

Patience is required. Lefties need Republicans to get on board. Then they need them to speak out. Then they need those Republicans to actually act, within their power, to oppose the president. Understand: Opposing your party's president is a near unnatural act in these tribalized times. That journey won't usually be accomplished in one step.

Trump opponents need to take what they can get. Jeff Flake's reasons for opposing President Trump won't be the same as the reasons at ThinkProgress. That needs to be okay.

This again is a problem with our failing pluralism: We Americans expect our allies to be our allies on everything — or else they're our enemies. A better approach would be to join forces when we agree, compromise as often as we can, and really only beat each other up over the relatively few uncompromisables. Instead, these days, we put everything in the "uncompromisable" category.

That way of doing politics, frankly, empowers President Trump.

"We cannot loudly and publicly say, 'Where in the hell are the Republicans who are willing to call out Trump?' then boo them when they do so," writer/activist Shaun King said Tuesday on Twitter. "When people you don't like do the right thing, the important thing, even if they've been enemies before, that's progress."

We don't have to forget that John McCain is overly hawkish, or that Bob Corker wanted to be Trump's secretary of state, or that George W. Bush was a historically awful president. But right now, the priority for lefties should be to contain and eventually end Donald Trump's presidency. They shouldn't be so eager to turn away allies. Liberals must learn to take "yes" for an answer.