Finally, on Monday Democrats agreed to a three-week extension of funding in return for a promise from Mitch McConnell, the Senate majority leader, of a vote on immigration legislation (we’ve heard nothing from Trump). If this vote doesn’t happen, we’ll be back to square one Feb. 8. Anyone want to take bets?

Basically, then, the government of the world’s greatest nation is lurching from crisis to crisis because its leader can’t be trusted to honor a deal. But what did you expect? Trump’s whole business career has been a series of betrayals — failed business ventures from which he personally profited while others, whether they were Trump University students, vendors or creditors, ended up holding the bag. And he hasn’t grown a bit in office, unless you count that mysterious extra inch.

There are two things you need to realize about Trump’s utter unreliability. First, it has ramifications that go far beyond the recent shutdown. Second, it’s made possible, or at least much worse, by his enablers in Congress.

Think, for example, about the international consequences of a U.S. president whose word can’t be trusted. Who can we count on to be a reliable ally, when no country knows whether America will stand by it if it needs help?

So far, at least, financial markets continue to regard the U.S. government as trustworthy, even though during the 2016 campaign Trump openly talked about forcing the nation’s creditors — like creditors of some of his businesses — to accept less than they were owed. But does this government have any reserve of financial credibility if something should go wrong? Probably not.

In other words, Trump’s unreliability is a big problem, over and above the substance of his policies. But here’s the funny thing: While his instincts are clearly autocratic, the Constitution doesn’t set him above the law. Congress has the power to constrain his actions, to force him to honor promises. His ability to keep betraying those who trust him depends entirely on the willingness of Republicans in Congress to go along.

For example, any two of the Republican senators currently wringing their hands over the betrayal of the Dreamers could have forced action by withholding their votes on the Trump tax cut. They didn’t. Similar inaction explains why Trump has been able to violate all previous norms against exploiting his office for personal gain, and much more.

The result is that promises from the U.S. government are now as worthless as those from a tinpot dictator. We don’t yet know how high a price we’ll pay for that loss of credibility, but it probably won’t be small.