One of the most embarrassing moments of the extremely embarrassing Barack Obama presidency came in the context of the Syrian civil war. In August 2012, Obama vowed that “a red line for us,” which would thereby necessitate some sort of American intervention, “is we start seeing a whole bunch of chemical weapons moving around or being utilized.” The 44th president continued: “That would change my calculus.”

Except it didn’t.

A year later, former Iran- and Russia-backed Syrian strongman Bashar al-Assad crossed Obama’s “red line,” launching a lethal sarin gas on his own people. Hundreds, perhaps thousands, were killed, including many children. In response, the Obama administration initially uttered a few tough words before quickly reaching a deal with Assad patron Russia, under which the Kremlin would be responsible for overseeing the surrender and eventual destruction of Assad’s chemical weapon stockpile. The result was a “red line” flagrantly crossed and a tremendous blow to American credibility on the world stage. Obama’s presidency never recovered.

Now, over a decade later, President Donald Trump risks repeating Obama’s mistake. The stakes are high.

On Jan. 2, Trump wrote on his own platform, Truth Social: “If Iran shots (sic) and violently kills peaceful protesters, which is their custom, the United States of America will come to their rescue. We are locked and loaded and ready to go.” He has followed up on that threat multiple times, including a post earlier this week that read: “Iranian Patriots, KEEP PROTESTING — TAKE OVER YOUR INSTITUTIONS!!! Save the names of the killers and abusers. They will pay a big price. I have cancelled all meetings with Iranian Officials until the senseless killing of protesters STOPS. HELP IS ON ITS WAY.”

It’s impossible to avoid the obvious implication of these statements: If the Islamist regime’s slaughter of its own citizens continues, the U.S. will take some unspecified — but clearly major — action to stanch the bloodshed. Trump encouraged the protesters to keep on risking their lives for freedom, in the face of wanton Islamic Revolutionary Guard Corps repression, because help is coming soon from Uncle Sam. What’s more, the regime’s massacres have dramatically escalated since Trump’s initial warning. There are no reliable numbers, but rough estimates suggest the number of Iranians killed by the regime has risen from 500-600 two weeks ago to potentially as many as 20,000-plus today.

To be sure, I am not a big proponent of drawing “red lines” in foreign policy. I subscribe to the notion, advanced by Alexander Hamilton in The Federalist No. 70, that the advantage of executive “unity” is that “decision, activity, secrecy, and despatch will generally characterize the proceedings of one man in a much more eminent degree than the proceedings of any greater number.”