In eastern Syria last week, American air and ground forces attacked Syrian pro-government military units, killing roughly 100 people, including some Russian advisors. U.S. Army Colonel Thomas Veale described the attack as “taken in self-defense.”

“Self-defense”? Had the regime of Bashar al-Assad bombarded Boston Harbor? No, but it had attacked a base, long held by Syrian rebels, with U.S. military advisors present. Despite the tit-for-tat chronology here, it’s hard to see how Veale’s “self-defense” claim is tenable.

After all, as Secretary of State Rex Tillerson explained last month, the Trump administration has committed to an indefinite military presence of roughly 2,000 U.S. boots on the Syrian battlefield. Are these troops present at the behest of the host government? Certainly not. Has Congress ratified their deployment in some way? Guess again. Are they there preempting an imminent threat of attack on America? Nope. Are they under the mandate of a UN Security Council resolution? No.

In fact, the U.S. military presence in Syria has no legal authorization whatsoever. Those American forces are cooperating with Syrian rebels to, as Tillerson put it, “help liberated peoples” in territory outside Assad’s control “stabilize their own communities” and defend themselves against regime forces. This is, he added, “a critical step to creating the conditions for a post-Assad political settlement.”

Dispensing with the euphemistic flummery, U.S. forces are engaged in a kind of creeping regime change operation—the lessons of recent history be damned.

One might fairly argue that the Assad regime, in its brutality against its own people, long ago forfeited the sovereign right to defend its territory against an invading foreign army. Fine, but we should be clear that Washington, in responding to the lawlessness, is also acting lawlessly—hardly a lodestar mission of the liberal, rules-based world order America claims to lead, and, in the big picture, decidedly not a case of “self-defense.”

Quaint legalisms aside, the clash between U.S. and Syrian forces should make clear just how dangerous our military presence in Syria is. This particular incident, we can reasonably assume, didn’t escalate only because the regime is desperate to avoid escalation. Were they to counterattack, the Syrians surely know, the full might of America would come crashing down upon Damascus, and that would be the end of them all.

But that is by no means a reassuring “balance of terror,” the term nuclear strategist Albert Wohlstetter used to describe the deterrence model of the Cold War’s mutually assured destruction. Indeed, the multi-sided chaos of the Syrian Civil War is neither balanced nor stable and the risk of escalation is very real. Should the actors in the next clash miscalculate, will the Russians defend their ally in Damascus before it falls, or will America’s “self-defense” spiral into the destruction of the regime? Will the resulting anarchy plunge us into a full-scale occupation? Will Turkey take advantage of the mayhem to rampage through Kurdish-held Syria? Will Iranian-backed militias still prioritize fighting Sunni extremist groups? If anything could reverse the defeat of the Islamic State, it is an escalation like this.

As with much of American foreign policy today, the threat to the United States in Syria is roughly proportional to the extent to which we choose to expose ourselves to it. None of the five missions Tillerson laid out for the U.S. military effort in Syria—to defeat ISIS and al-Qaeda, usher in a post-Assad state, counter Iranian influence, facilitate the return of refugees, and free Syria of weapons of mass destruction—are vital to protect America’s wealth and physical security.

Nor are these low-cost, low-risk, or high-probability-success missions. And as everyone knows, the last thing America needs now is a new set of elective, hazardous, and unachievable war aims on the other side of the globe.

America has an interest in a stable Middle East, and thus in a stable Syria, but the notion that U.S. policy has contributed to that end is rather dubious. The Islamic State, which exacerbated the Syrian Civil War by orders of magnitude, is, after all, an outgrowth of America’s war in Iraq. And the U.S. and its allies encouraged the Syrian rebellion from early on, an effort that was not only a spectacular failure but also fostered quite the opposite of stability.

An enduring feature of U.S. foreign policy is that each intervention, whether it is seen to fail or succeed, eventually serves to justify further intervention. While it’s true that the Islamic State has been decimated, thanks in part to the collective destructive power of Damascus, Tehran, Baghdad, Moscow, Washington, and various Kurdish and Syrian militias on the ground, it has been accomplished at great cost in blood and treasure. The answer to this near-Pyrrhic victory is not for Washington to invent new missions that lack legal authorization or a plausible timeline of success, but instead to reckon with its own role in this interminable tempest and acknowledge the very real possibility that backing away may be in the best interest of America and of Syria.

John Glaser is director of Foreign Policy Studies at the Cato Institute.