Why should anyone trust Donald Trump not to sell out on immigration control if he’s elected? Good question! One reason is he’s so heavily invested in the issue — it’s been the rocket fuel of his rise — that he couldn’t reverse course without losing much of his support overnight.  But I think there’s a concrete, realpolitik underpinning for this calculation. It’s this: Trump has no institutional base of support. Democrats hate him. The Republican party apparatus hates him. Lots of elected Republicans hate him. That means, if as president he infuriates the ordinary voters who support him, he’ll be at risk of more than just upside down poll numbers. He’ll be at risk of impeachment — more so than just about any potential president you can think of.

What if Trump takes the oath of office and declares:

“I’ve evolved. I think building a wall on our Southern Border isn’t a good idea. I mainly brought it up just to get people’s attention.”

A firestorm ensues. Voters who liked Trump are hanging him in effigy; those who disliked Trump are saying, “We told you so.” Who’d support Trump if someone in Congress pushed for an impeachment vote?**  House Republicans terrified of being “Cantored.” No. Democrats? Maybe some Democrats — but they are hardly Trump’s friends, and not just because of immigration. They’d have to worry about the new president compensating for his flip-flop by placating the right on a host of other issues (including Supreme Court nominations). Plus they’ll have just spent four months arguing Trump is unfit for office. This would be a chance to get him out, perhaps with William Henry Harrisonesque efficiency.

It only takes a House majority to impeach, remember ( and subject the president to a Senate trial). Nancy Pelosi would have Trump’s fate in her hands — and in exchange for saving him, she might demand concessions that would only make Republicans more eager to be rid of this interloper.

It would be a hell of a negotiation — one presidents who do have institutional backing*** don’t have to worry about.

Easier just to build the wall.

P.S.: Given the heightened impeachment threat, if I were Trump I’d make sure my vice-presidential pick was someone Democrats in the House (and half the Republicans) would really not want to see become president.

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**– Is revealing that you’ve won the presidency on false pretenses a “high crime [or] misdemeanor”? Doesn’t seem a crazy idea to me. A deception of that magnitude would arguably be more damaging to the Republic than, say,  perjury in a civil deposition.  In any case, the definition of “high crimes and misdemeanors” is effectively up to the House, no? Which means Trump would have to worry about it.

***– Wouldn’t Cruz be subject to the same threat? I doubt it. a) If he won, it would be because the GOP establishment rallied behind him; b) Cruz’s supporters can’t possibly have as high expectations of him, on immigration, as Trump’s supporters have of Trump. The requisite intensity of outrage would be lacking — as it would be if Trump reversed himself on a less salient promise, such as his pledge to repeal Obamacare.