President Donald Trump has vowed to retaliate after Iran shot down a U.S. Apache helicopter, but it’s unclear what that response will mean for the state of negotiations and the war.

U.S. military personnel in the region have come under repeated Iranian attacks despite the ceasefire agreement Trump announced on April 7, and they have defended themselves and responded in kind. But the shooting down of a U.S. Army AH-64 Apache on Monday, and Trump’s subsequent promise to “respond to this attack,” raises additional questions about the state of the conflict moving forward.