President Trump and (left to right) Jeff Flake and John Kasich (Yahoo News photo Illustration; photos: AP, Getty)

A week ago, I wrote about the damning silence of Republicans in Washington when it came to the Trump presidency. In the days since, it’s gotten a bit noisier.

Even as I was writing that column, John McCain — the good old plainspoken McCain we’ve known for most of his public life, not the evil twin who has occasionally tried to sidestep his conscience — issued a crisp rebuttal of Trump’s isolationist worldview and contempt for public servants.

Then George W. Bush, the retired and retiring former president, resurfaced to deliver a remarkably eloquent speech in which he slammed “nationalism distorted into nativism” and lamented a “discourse degraded by casual cruelty.” Neither McCain nor Bush mentioned Trump by name, but neither had to.

All that had barely sunk in when Trump set about attacking Republican Sen. Bob Corker again, and Corker — who had already shared his fear that Trump could bumble into World War III — accused Trump of “debasing our country.”

And then came an absolutely stunning rebuke of the president on the Senate floor by Jeff Flake, the Republican senator who recently wrote a book challenging Trump’s brand of conservatism, and who announced he would stand down for reelection rather than “be complicit” in the direction of his party.

You should take the time to read Flake’s speech for yourself, but here’s my favorite passage:

“We were not made great as a country by indulging or even exalting in our worst impulses, turning against ourselves, glorifying in the things that divide us, and calling fake things true and true things fake. And we did not become the beacon of freedom in the darkest corners of the world by flouting our institutions and failing to understand just how hard-won and vulnerable they are.”

Trump and the island of misfit toys that serves as his senior staff probably considered this a pretty good week. That neither Corker nor Flake is willing to risk a primary for his seat demonstrates the abiding passion of Trump’s base in conservative states. No doubt he hopes to replace them with allies, and he might.

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But I’m guessing Trump will look back on this period as the moment when something ominous started to cohere in the Republican ranks. Because this president is headed for a serious, inevitable primary challenge — perhaps more than one. And it could be Trump, sometime in 2019, who ultimately decides to back away.

I know this might sound implausible (or maybe wishful, depending on your politics). We’ve seen modern presidents challenged in primaries before — Ford, Carter, the first George Bush — without any of them losing, and you’d have to go back a half century to find one (Johnson) who was forced to withdraw. Trump’s standing among Republican voters still looks pretty darn strong, at least on the surface.

And Trump already clobbered his party’s leading senators and governors in a bunch of contested primaries once, so it seems reasonable to think he would do it again.

Astute observers of politics will point out — as I have many times — that grassroots movements always come from the ideological extremes, rather than from party establishments. There are no centrist revolts in American politics, although there are plenty of sober symposiums attended by budget scolds and newspaper columnists.

But we’ve never had a president like Trump. And the thing we know from his ascent is that the rules as we once applied them are a pretty poor predictor of what happens next.

Trump isn’t Ronald Reagan or even Pat Buchanan; his conflict with the Corkers and Flakes of the world, which is almost certain to expand in coming months, isn’t the usual face-off between strident right and mushy center. It’s not about any discernible ideology at all.

No, this is about furthering a policy agenda, on one hand, versus an agenda to expand the Trump family brand on the other. It’s about Trump’s celebrity and his contempt for politics versus the wing of his party that aspires to govern.

So we’re not talking about a primary campaign fueled by the passion of boring centrists preaching deficit reduction to the fired-up masses. We’re talking about longtime activists, big contributors and local officeholders who think the party has to be rescued from the Trump Organization before it goes the way of the Whigs.

No one’s going to take on Trump with a slogan that says: “Preserve our vulnerable institutions.” But “Take our party back!” is just about the most powerful appeal in modern politics, and that’s one you might hear a lot.

Could it actually resonate among Republican primary voters?

Not if you buy the most common narrative in the political media, which holds that Trump stormed the party and confounded the analysts, winning over the base with his nativist appeal and stomping all over his establishment rivals. Trump was a juggernaut, a hero to the furious masses.

Well, OK. But here’s an alternative theory that I think closer to the truth.

Trump ran against something like 10 serious candidates, because the new campaign finance rules encouraged everybody with a rich buddy to run, and all of them scrambled for the same airtime and the same voters, while Trump’s shameful appeal to intolerance, along with his TV and Twitter celebrity, landed him a modest plurality of unshakable voters.

It wasn’t until deep into the primaries, with his nomination a foregone conclusion, that Trump finally managed to sway a majority of Republicans to his side. He didn’t storm the fractured party establishment; he outlasted it.

The math looks very different when you’re running against only one candidate from the start, or even two. An enraged, nativist 30 percent won’t get it done.

The traditional Republican electorate, rallied behind a single challenger in the name of restoring dignity and greatness to the party, might create a surprisingly strong counterforce to the dwindling audiences at Trump’s rollicking rallies.

As for Trump’s ironclad support among Republicans now, it only looks that way because voters are assessing him in opposition to two institutions: Democrats and the media. Next to those two, Trump looks to most Republicans like George Washington.

But as this very sharp Washington Post analysis laid out this week, better polling — in this case done by Pew Research — tells a different story. Even the most reliable Republican voters are as likely to disagree with Trump on the issues as agree with him, and they’re more likely to be conflicted about his personal behavior than they are to approve.

In other words, Republicans stand with Trump, but they don’t much like him. They’re more than willing to believe that another Republican would be better. In fact, core conservatives remain far more bullish on Vice President Pence than they are on Trump.

Pence isn’t a likely primary opponent right now, but a conservative critic like John Kasich might do a lot better with an undivided primary electorate than he did the first time out (unless he decides to bypass the primaries and run on an independent unity ticket, instead). A new voice like Ben Sasse, the senator from Nebraska, might exploit that opening, or maybe someone else we haven’t even thought of yet.

Or maybe that’s the path Jeff Flake himself was tilting at in his speech this week, when he said: “To be clear, the anger and resentment that the people feel at the royal mess that we’ve created are justified. But anger and resentment are not a governing philosophy.”

If you’re looking to launch a campaign against Trumpism, that’s not a bad place to start.

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