Don’t look to the Constitution to stop this

My 10-year-old put it best: 'First you said Trump wouldn't win any primaries. Then you said he wouldn't win the nomination. So why exactly are you so sure he won't become president?' Given this reasonable question, it's time to start asking: Is the Constitution in danger from a Donald Trump presidency? How far can he push the envelope of our constitutional structure and traditions?

To be clear, I'm not talking about who Trump would nominate to the U.S. Supreme Court. Though it's worth noting that, unlike potential running mates who so far seem wary of a poisoned chalice, judicial nominees would probably be glad to serve if named by Trump. He'd already be president; and once confirmed, they'd no longer be beholden to the man who named them.

The real threat seems to be that the candidate who has made it this far by throwing out the election rulebook would be inclined to do the same with the rules of governance. I think we can usefully break up the question into domestic policy and foreign policy components. In each instance, there are practical limits.

Start with the home front. It seems likely that Trump would have a hard time passing domestic legislation, since he may face a Democrat-controlled Senate and a House full of hostile Republicans. But to Trump, that might be an invitation to action rather than a constraint. He'd start with unilateral executive action, which certainly is his style.

As President Barack Obama has demonstrated with his immigration initiative, an executive order can go pretty far if it's framed as prosecutorial discretion. Trump could announce, for example, that he wants the Internal Revenue Service to stop auditing people. He's been audited enough himself that this seems plausible.

Democrats would find themselves in an awkward position if that happened. They've been arguing that Obama's discretionary authority allows him to exempt a large class of undocumented people from deportation. It would be tricky now to say that the constitutional requirement that the president 'take care' that the laws be faithfully executed restricts Trump where it doesn't restrict Obama.

The Department of Justice's Office of Legal Counsel, traditionally independent-minded, could tell Trump that a given executive action goes too far and is unlawful. But the same office told George W. Bush that the CIA could waterboard captives. And it told Obama he could target and kill a U.S. citizen abroad without a trial. So it's subject to political vicissitudes. And Trump would be sure to appoint a head with strong pro-executive power views.

One limit to selective prosecution would be the equal protection guarantee of the 14th Amendment. If a defendant could show that prosecution decisions were being made on the basis of, say, race, then a court could potentially intervene. The standard of proof is very high, however. Implicit racism isn't sufficient, nor is statistical evidence showing a generic racial disparity.

The Supreme Court has said, in the 1999 case of Reno v. Arab-American Anti-Discrimination Committee, that targeting foreign nationals for deportation on the basis of their views wouldn't count as selective prosecution, provided they are otherwise eligible to be deported.

As for U.S. nationals, there's a strong tradition against selective auditing or prosecution on the basis of politics. But as a matter of constitutional law, criminal or civil prosecutions can be made at least partly on the basis of political judgment so long as it isn't demonstrably driven by animosity. A prosecutor could go after big-wigs because she just doesn't like them, or because she thinks convicting them would send a good message. Trump could therefore potentially appoint U.S. attorneys and direct them to prosecute people he doesn't like. Again, there's a tradition of U.S. attorney independence — but it's a tradition, not a law. The international sphere gives Trump still more space to maneuver. In theory, he would need congressional authority to go to war. But Obama is fighting Islamic State without any express authorization. The president claimed that bombing Libya didn't count as hostilities for purposes of the War Powers Act. And Congress hasn't done anything about it.

It follows that about all Congress could do to block Trump from various hostilities would be to deny funding for his operations.

The same would likely be true of a wall on the Mexican border. The president likely has enforcement authority to build the wall. He just needs money.

Of course, Trump has famously said he will make Mexico pay for the wall. That might let him get around Congress. As president, he can meet world leaders and try to make them do what he wants — and the Constitution is behind him.

Some of Trump's ideas for the military would violate international humanitarian law. No doubt some or (one hopes) many military personnel would refuse to follow illegal and immoral orders; for example, to kill terrorists' family members.

But it's worth noting that the Constitution as usually interpreted doesn't bind the U.S. to follow international law, including the Geneva Conventions. Some provisions of international law can be found in statutes, which would bind the president and the armed forces. But not all international law violations are domestic crimes.

Last to consider is trade. Trump can't impose tariffs on his own without Congress. But many trade laws give the president executive authority to make determinations about whether other countries are in compliance. That gives the president discretion again.

Expect Trump to use that discretion — and expect the legal system to let him.

Noah Feldman is a columnist for Bloomberg View.