Checks and balances

Who's going to stop them? I mean physically, because words won't.

I would hope the Constitution might. We'll have to depend on the judiciary branch.

The last thing that's going to stop him is some old words on parchment. The judiciary sounds like an option, until you realize there's absolutely nothing they can nor will try to do to stop him. The Supreme Court may tell him no, but they gave him immunity anyways, so basically he's free to do whatever he wants, and he will.

That immunity should have its limits.

It's his Supreme Court, so of course the decision was to be expected