We’re actually doing “red line” nonsense again with Syria, five years after Obama’s fiasco over that? Read this from last night if you haven’t already. The closest the U.S. came to attacking Assad under Obama was after a chemical attack in August 2013 in the suburbs of Damascus that killed many more people than Monday’s attack in Idlib did — and Trump spent the following weeks full-throatedly warning Obama not to get involved. What’s changed, except for the fact that now it’s Trump himself who stands to look feckless if he does nothing?

Here’s the best he could do to explain his change:

Trump on Syria: "I do change and I am flexible. It's very very possible that my attitude toward Syria and Assad has changed very much"

— John Harwood (@JohnJHarwood) April 5, 2017

Again, the Damascus attack in 2013 killed upwards of a thousand people, mainly women and children, and Trump couldn’t have been clearer at the time about opposing intervention. For sound reasons too, per his tweets: Any collateral damage in attacking Assad would be used against the U.S. as propaganda; even a small, supposedly limited intervention could easily balloon into a much longer, more expensive one; we might inadvertently strengthen jihadist forces there by damaging Assad, and so on. All of those cautions still obtain — except now they’re balanced against Trump’s personal prestige as a strongman. So here he is preaching “red lines” in vintage Obama mode instead of hooting at Obama to stay out of Syria.

So now, after criticizing Obama yesterday (and again today) for not enforcing his own red line in 2012, he has to act. To do nothing after this red-line song and dance would make him look weaker than even O. In theory he could act diplomatically, not militarily, but I don’t know what remaining diplomatic levers exist to punish a rogue regime like Assad’s, with whom the U.S. already has no relations. If Trump’s hoping the UN will do something, he’s in for hard lesson on how the Security Council works when Russia inevitably exercises its permanent veto against any multilateral action against Syria. And what about Trump’s hoped-for Russia diplomacy? If he acts unilaterally against Assad, we risk ending up on the wrong side of Russia in a hot war. I hope he thought through the implications of the “red line” business here more than his predecessor did.

Update: Free spin: Next time he’s asked why his position on Assad has changed, he should cite the failed disarmament compromise after the 2013 Damascus attack. Obama agreed to hold off on bombing in return for Assad agreeing to give up his chemical weapons. Clearly Assad lied; now we get rough. The only wrinkle there is that it’s Trump’s would-be buddy, Vladimir Putin, who brokered that disarmament agreement. If Trump pronounces it a sham in light of recent events, he’s implicating the Kremlin in that sham too.

A reporter asks Trump if the chemical attack in Syria crossed a red line: "It crossed a lot of lines for me" pic.twitter.com/xQPhr7IeKu

— POLITICO (@politico) April 5, 2017