Donald Trump has won the election. Now it is up to America’s institutions, and the people within them, to check his worst instincts.

There is danger in Trump. He’s a man with authoritarian impulses, a conspiracy theorist’s bent, and a taste for vengeance. He has an alarming temperament, little impulse control, and less decency. He has a demagogue’s instinct for finding enemies and a bully’s instinct for finding their weaknesses. He is uninterested in policy, unrestrained by shame, and unbound by norms. He surrounds himself with sycophants and enablers, and he believes both the facts and the falsehoods he finds congenial.

But he is entering an office that is weaker than many realize. For all the same reasons Barack Obama could not bring about the change he had made people believe in, Trump cannot wrench America to his vision of greatness. He is constrained by the House and the Senate, by the Supreme Court, by the executive agencies, and — in ways less formal but no less powerful — by his own staff and party.

There would be more comfort in this if there were more opposition inside these institutions. But Republicans control everything — the House, the Senate, and, after an appointment, the Supreme Court. If Trump is to be checked, it will be because his own party checks him.

So far, the GOP has not shown much interest or ability in standing up to their standard-bearer. Top Republicans closed ranks around Trump despite believing him fundamentally unfit for office. Their embrace did not, however, lead to Trump surrounding himself with more professional staff, developing sounder policy, or moderating his worst instincts.

Already, the Trump campaign has leaked that they will fill their administration with the most supportive staff they can find, not the best. But the number of jobs they appear to have candidates for is slim. They will need many more bodies to fill both the White House and the executive agencies. This is a place where the Republican Party could potentially play a role in surrounding Trump with calmer, wiser advisers who could provide him better information and curb his worst impulses.

The Republican Congress will use Trump to pass the agenda it has already crafted — Paul Ryan’s bargain has always been that he will endorse a man he clearly believes to be dangerous so long as that man appears likely to sign his budget. Trump is a dealmaker, and he’ll presumably hold up his end of the deal. The question is whether Congress will attempt to check Trump elsewhere — on surveillance, on wartime powers, on trade.

But our institutions are only as good as the people running them. Parties have strong incentives to back their president — that’s how Trump united the GOP after he became the nominee, and it’s how he’ll hold it together after he takes the White House. There’s been little evidence that Republicans — even the ones who clearly recognize Trump’s danger — are willing to risk electoral sanction to protect the country they profess to love.

House and Senate Republicans know that Trump’s success is their success, that his strength is their strength. The same goes for his staff, and his appointees. The question is whether they can structure a version of success for him that keeps the country safe, and whether they will be willing, if the worst comes to pass, to cross their president for their country.

If there is hope, it is here: The incentives of governance are different from the incentives of opposition. The Republican majority will have to face the voters in 2018, and then again in 2020. If they have taken health insurance from tens of millions of people without replacement, if they have ripped open families and communities with indiscriminate deportation, if they have embroiled us in disastrous wars or confrontations, if they have sent the economy into tailspin, those elections will not be pleasant.

Perhaps this is a weight Trump will feel in a way he has not over the course of the campaign, and he will change his behavior accordingly. But even if he doesn’t, Republicans have a majority, and it will be one they hope to keep. To keep it, they will need to govern well, or at least convince the electorate they have governed well. And to govern well, they will need to keep Trump’s worst tendencies in check. Now we see how strong the American system really is.