In the 15 months since the president unilaterally launched our latest war in the Middle East, he’s repeatedly pledged that he wouldn’t put US “boots on the ground” in Syria.

As he told congressional leaders on September 3, 2014, “the military plan that has been developed” is limited, and doesn’t require ground forces.

Alas, if you liked that plan, you can’t keep it. Earlier today, the Obama administration announced the deployment of US Special Forces to Northern Syria to assist Kurdish troops in the fight against ISIS.

US forces will number “fewer than 50,” in an “advise and assist” capacity; they “do not have a combat mission,” according to White House press secretary Josh Earnest. Granted, when “advise and assist” missions look like this, it can be hard for us civilians to tell the difference.

Asked about the legal authorization for the deployment, Earnest insisted: “Congress in 2001 did give the executive branch the authority to take this action. There’s no debating that.”

It’s true that there hasn’t been anything resembling a genuine congressional debate over America’s war against ISIS. But the administration’s legal claim is eminently debatable.

It’s based on the 2001 authorization for the use of military force, or AUMF, the Congress passed three days after 9/11, targeting those who “planned, authorized, [or] committed” the attacks (Al Qaeda) and those who “aided” or “harbored” them (the Taliban).

In 2013, Obama administration officials told the Washington Post that they were “increasingly concerned the law is being stretched to its legal breaking point.” That was before they’d stretched it still further, 15 months later, to justify war against ISIS, a group that’s been denounced and excommunicated by Al Qaeda and is engaged in open warfare with them.

Headlines like “ISIS Beheads Leader of Al Qaeda Offshoot Nusra Front,” or “Petraeus: Use Al Qaeda Fighters to Beat ISIS” might give you cause to wonder — or even debate! — whether this is the same enemy Congress authorized President Bush to wage war against, back before Steve Jobs unveiled the first iPod.

In the Obama theory of constitutional war powers, Congress gets a vote, but it’s one Congress, one vote, one time. This is not how constitutional democracies are supposed to go to war. But it’s how we’ve drifted into a war that the Army chief of staff has said will last “10 to 20 years.”

Sooner or later, we’ll have cause to regret the normalization of perpetual presidential war, but any congressional debate we get will occur only after the damage has already been done.

Cross-posted from Cato.org.