The reason, as I have written before, is that no president—not Barack Obama and not Donald Trump—has the authority under the Constitution to “declare war.” Of all the toxic constitutional developments of the Obama years, by far the most disheartening is this: Obama’s unlawful intervention in Libya garnered strong criticism; but the harshest criticism came when Obama chose to obey the Constitution by asking for congressional authorization to strike Syria. For breaking the mold of presidential unilateralism, he garnered—and continues to garner—the undisguised scorn not only of his political enemies but even of many of his friends. That hostile verdict on his presidential leadership is the clearest sign that we have entered what future historians may describe as a post-constitutional era.

Why, of all the many military misadventures into which Uncle Sam has blundered since 2001, is Syria different? The reason is that, under the Constitution and the War Powers Act, the president has no authority to send military forces into hostilities except after congressional authorization or in response to a direct attack on the U.S. or its forces. The president has no inherent power over war; it is given to Congress. In 2001, George W. Bush grumbled about his supposed executive authority, but went to Congress for approval of a “war” against “those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001”; in 2002, he did the same again, and got approval to “defend the national security of the United States against the continuing threat posed by Iraq; and … enforce all relevant United Nations Security Council resolutions regarding Iraq.” Those resolutions remain, at least technically, in force, and have been used by the Obama and Trump administrations as justification for U.S. efforts on behalf of forces—including some of the Syrian rebels—fighting against the Islamic State, supposedly a “successor” to Al Qaeda.

Republicans in the congressional leadership insist that the 2001 authorization is all that’s needed. “The existing AUMF gives him the authority he needs to do what he may or may not do,” House Speaker Paul Ryan said Thursday. That plough really won’t scour, no matter how you torture the text. The nation of Syria is not the nation of Iraq; and the Syrian government is not Al Qaeda, nor an affiliate, nor a successor, nor anything except a sovereign nation against which the president has decided to go to war.

Trump must go to Congress to seek approval now; and if he does not, Congress must, regardless, conduct a full debate on what he has done and whether he should be allowed to keep doing it and when he should stop. Trump is both incoherent and pathologically secretive. He is almost certainly unable and unwilling to tell the country what he is doing. If Congress does not debate the next step in Syria, there will simply never be any statement of U.S. war aims. Neither the Syrians, nor the Russians, nor any U.S. allies, nor the American public will have a clue what we are doing and when we have failed or succeeded.