Barack Obama did the right thing Saturday, on a number of levels. The first and most obvious one: The Constitution calls for it. Yes, we’ve got a history now of more than 50 years of presidents not going to Congress. One of them is named Obama (on Libya). But today he did the right thing by the Constitution: “Having made my decision as commander-in-chief based on what I think are our national security interests, I’m also mindful that I’m the president of the world’s oldest constitutional democracy.”

Well said. Kind of sad that it’s so stunning and refreshing to hear a president acknowledge that he shares constitutional power, but stunning and refreshing it was. This precedent will now be cited by congresses well into the future whenever a president wants to undertake a jolly little shoot-up—he’ll need to go to Congress first (for big, real, ground-troop wars, the pressure to consult Congress will always be great). It’s a big relinquishing of power, a major constitutional recalibration that will outlast him and the yahoos whose votes he’s going to be seeking, and Obama deserves props for it.

It was also manifestly clear that this is what the public wanted him to do—79 percent, in yesterday’s NBC poll. If he had launched a strike without consulting Congress in the face of those kinds of numbers and something went really wrong, look out. That way leads political calamity and, as I wrote on Friday, possibly impeachment. So it’s smart in terms of self-preservation as well as principle.

Finally, in terms of the domestic political interpretation of any potential military action, no matter what he does, Obama can’t lose. If Congress says no (more on which in a moment), then he doesn’t have to launch a strike that is making Americans very jumpy. If it says yes, then public opinion will presumably come around, and probably world opinion, too, in the 10 or so days between now and the House vote.

So those are the upsides. Now let’s do some nose-counting. In the Senate, I presume a resolution will pass. Obama might lose a very small number of Democrats, and maybe Independent Bernie Sanders. But he should get several Senate Republicans—McCain and Graham, their buddy Kelly Ayotte, probably Lisa Murkowski, Bob Corker, a few others who aren’t up for reelection this year and in hiding from the tea party. McCain and Graham will push Obama to do more than he wants, to do a strike that could lead to regime change, but one would hope they can agree on language to make both sides happy. Harry Reid said Saturday he’d try to bring the Senate back early for a vote, meaning it will say yes first, adding to the drama as we turn to the House.

There? Yesterday, I thought the chance the House would pass a war authorization for this president was about 0 percent. Today I’ve revised that up to about 5 percent. I think a certain number will be so favorably impressed/shocked by Obama’s decision to consult them that they’ll be inclined to give him the benefit of the doubt.

I still consider approval a real long shot, though. Consider first the number of possible Democratic defections. So far, we know that 18 Democrats signed a letter circulated by Republicans stating that a strike undertaken without congressional approval would violate the Constitution. That concern is taken off the table, so maybe those 18 will play ball. But you have to think that maybe a couple dozen of the most liberal members, representing districts where three-quarters of their constituents are telling them no, will vote against.

If I’m right about that, it would mean that Obama would need around 45 Republican votes. Possible? I guess. But keep an eye over the weekend on how ferociously the media wingnuts start whipping this vote. What’s Rush Limbaugh going to be saying? He is also bereft of the constitutional argument now, of course, so what’s his new excuse going to be and how hard is he going to push people to oppose a strike? Rand Paul and the other libertarians? The various tea party movements?

I genuinely don’t know. It will be fascinating to watch. Obama said that he’s going to share the evidence with Congress. Will the evidence be persuasive? Remember, it only has to be persuasive to about one in six of them. For most of them, this vote is a chance to humiliate Obama before the entire world. That’s an opportunity that’s just going to get right-wing juices flowing furiously, and most of them will inevitably vote that way. But I suppose a narrow pro-strike vote is possible.

And what does Obama do if the Senate votes yes by a fairly strong margin, say 62 to 38 or so, and he loses narrowly in the House, by fewer than 10 votes? Could he say in essence, well, I consider the overwhelming Senate vote more binding than this razor-thin House vote? That’s not impossible, either.

Final question, and in many ways the most important one, in that it’s not about U.S. politics but about the actual thing at hand: What’s Bashar al-Assad going to be spending the next 10 days doing? Is he going to be nervously pacing the palace? Is the slaughter going to intensify or abate? Is he enough of a madman to use chemical weapons again in the next few days? Anything like that would seem a clear signal that he—and Iran—want to draw the United States into conflict. But it seems more likely his moves will be defensive, moving things around.

Obama is still in a spot. After all, he might be forced into a position where, after all this tough talk about century-old international norms, he can’t take action. Depending on how things play out, this could do enormous damage to his international standing. And more importantly, Assad would go unpunished. All of which makes this week one of the most important in Obama’s tenure. The argument to the Republicans in the House and the American people is simple. He’s fulfilled his constitutional duties. Will Congress fulfill its moral ones, or is their hatred of Obama so great that they will instead choose the side of a monstrous murderer?