Last night a friend, a staunch populist conservative, texted to say, “We are having our Caligula moment.” The Trump thing, of course. I thought of that reading Andrew Sullivan’s column this morning, especially these paragraphs:

The core concern was always deeper than this. It was that Trump doesn’t understand the Constitution he has sworn to protect; that he would abuse his executive power, to lash out at enemies; that he would undermine the rule of law by trying to get his way, consequences be damned; that he would turn vital democratic institutions, such as the Justice Department and the FBI, into mere handmaidens of his own interest, rather than guarantors of the public’s. And it is clear to me that the firing of Comey — while within the president’s Constitutional powers — falls squarely into this category. To fire someone who is conducting an investigation into your own campaign cannot help but be seen as an interference with the rule of law. It is to cast doubt on the integrity of that investigation, and its future. It undermines public confidence that the executive branch can enforce the law against itself. It politicizes what should not be politicized. It crosses a clear line.

And it also crosses a line when you keep lying brazenly about why you did it. You don’t pin it on Rod Rosenstein. You don’t pretend it’s about “showboating.” You don’t ludicrously argue that you’ve just finally realized that Comey did Hillary wrong. You don’t also say that you were going to fire him anyway. You don’t say the FBI was in turmoil under Comey, when it wasn’t. And you don’t say you want to get to the bottom of the matter when you have already declared the entire story a hoax. More to the point, you don’t lie about all these things and then go on television and blurt out the truth: “When I decided to just do it [fire Comey], I said to myself, I said, you know, this Russian thing with Trump and Russia … is a made up story, it’s an excuse by the Democrats for having lost an election.” Read that again. The president has just said on national television that the Russia investigation was in the front of his mind when he decided impulsively to fire Comey. He has admitted he wanted to remove the FBI director because his investigation — which is fast intensifying — was targeting his campaign. That is called obstruction of justice. His spokeswoman yesterday reiterated that, after the Comey firing, the administration hoped the Russia investigation, which was trivial, would be wound up soon.

Sullivan is right about this. Like Sullivan, I am skeptical that there is a smoking gun in the Russia inquiry, and I believe that Comey has made mistakes that could justify his dismissal. But Donald Trump has now admitted openly that frustration with the FBI investigation of his own campaign led him to fire Comey. Sullivan says that’s obstruction of justice that requires impeachment.

I don’t know if that constitutes actual obstruction of justice, and even if it did, there is no chance that the Republican Congress will file articles of impeachment against Trump. But give Trump time. That he behaved this way last week is clear evidence that everything in the first line of the Sullivan passage I quoted is true. Trump cannot help himself. If the nation finds itself at this place only four months into the Trump presidency, and nobody around Trump had the power to stop him from doing this, then is anybody willing to say that something like this will never happen again? This isn’t about preventing Trump from “draining the swamp,” or protecting the mandarins of the Beltway from populist challenge. This is about the rule of law, and a president who holds the norms of our democracy in contempt.

Republicans in Congress had better start asking themselves where the bright red line is. Maybe it’s when he appoints his horse as FBI director. Or Jared.