If Republicans are surprised that Trump betrayed them, they haven't been paying attention
This was entirely predictable
This was just the betrayal Republicans feared. President Trump, unmoored from ideological and partisan commitments, would one day toss them aside, sell them out, turn his back on them in order to make a deal with those diabolical Democrats. And so it has come to pass, in a dramatic White House meeting in which Trump decided to sign on with a proposal by Chuck Schumer and Nancy Pelosi to increase the debt ceiling for three months, instead of the 18 months Republicans wanted, paired with an aid package to repair the devastation of Hurricane Harvey and a temporary government spending bill to hold off a shutdown. His decision apparently came as a shock not only to the Republican congressional leaders in the room, but even to his own aides.
The cries of anguish and rage reverberated throughout the land. "He f---ed us," said one anonymous Republican official. "It's just a betrayal of everything we've been talking about for years as Republicans," said former Sen. Jim DeMint, who until recently led the conservative Heritage Foundation. "We are going to need a supplemental spending bill to lease more buses for Trump to throw us under," said a Capitol Hill Republican. Oh, the humanity!
But hold on a minute. What are we really talking about here? This is all because Republicans wanted to push the debt ceiling past the midterm elections so they wouldn't have to vote on it again — the same Republicans who pressed one debt ceiling showdown after another while Barack Obama was president. Was this really some kind of critical ideological test that Trump failed? Or was it just a relatively minor disagreement about the congressional calendar?
It does have some political consequences, but above all it shows that Republicans still don't understand Donald Trump.
The first thing that they may not get is that he doesn't really care about them and their fates. Republican leaders don't want to take more debt ceiling votes because of their own lunatic fringe, which is happy to push the United States to the brink of default if they might be able to use the crisis to squeeze out some cuts to the safety net (which is one of the reasons why we should get rid of the debt ceiling entirely). They don't want to have to face their own misinformed voters saying, "Why did you vote for more debt?" when that's not what increasing the debt ceiling means — a misconception they themselves have encouraged for years.
But Trump didn't much care. He wants to be seen as doing deals, and bipartisan deals are more newsworthy and notable than ones with his own party.
Second, Republicans are surprised when everything comes back to the personal with Trump. He's been perturbed by Paul Ryan and Mitch McConnell's inability to produce legislative "wins" for him — he and McConnell are barely on speaking terms, according to multiple reports ("It's fine," McConnell says unconvincingly of their relationship. "Everything's fine.") — and when Trump gets mad at you, he's going to screw you over, preferably in a way that involves public humiliation.
Part of Trump's personalization of politics is that he doesn't share his fellow Republicans' horror at the very idea of cooperation with the other side. Even though he relentlessly plays to his base and almost never offers Democrats anything of substance, he still likes the idea of working across the aisle. Other Republicans, shaped by the Obama years, find cooperating with Democrats to be inherently evil, regardless of whatever such cooperation might produce. There may be times when you have no choice, but if you can avoid it all all costs, you do. Trump doesn't have the same reluctance, so given the opportunity to make Ryan and McConnell unhappy and say to the cameras "I made a deal," he'll take it.
The odds that he has an actual opinion about the relative merits of a three-month increase versus an 18-month increase in the debt ceiling are near zero. The political subtleties of the current situation and the potential for a complicated set of challenges in December when the debt ceiling will have to be raised again are probably lost on him. But he knows he was mad at McConnell and Ryan, so making an agreement with the Democrats was kind of like a 5-year-old saying, "I wish Mr. Schumer and Ms. Pelosi were my parents!" when he didn't get to eat cookies for breakfast. Except this 5-year-old is the president of the United States.
Judging from the furious tone of the Republican responses to the agreement Trump made with Schumer and Pelosi, you'd think they had suffered some lasting defeat, and that Trump has revealed himself at last to be not the real ally they thought he would be. But that's not true either.
The fact that Trump doesn't care deeply about ideology or even partisanship means that every day is a new one. He hasn't made some ideological pivot, and there's no reason to think that he won't continue to pursue all the same policies he has pursued so far, whether it's dismantling environmental protection or doing favors for Wall Street or deporting immigrants. It just means that Republicans need to keep their eye on him every minute, because you can never be completely sure what he'll do.