SIXTEEN STATES, led by California, have filed suit in federal court to block any construction of a wall along the southern border using reprogrammed funds pursuant to President Trump’s declaration of a national emergency. Their complaint presents a persuasive case against the president’s move, to the effect that it runs contrary to the constitutional rule that the executive branch may not spend money without Congress’s permission. And, in this case, Congress has explicitly denied Mr. Trump funds to build any barrier except for 55 miles of bollard-style fencing in a specific area of Texas. Not only is there no national emergency, the complaint argues, but also the wall would not meet the definition of “military construction” in the statute Mr. Trump claims as authority for $3.6 billion of his proposed spending.

Convincing as they are in policy terms, however, the states’ arguments face an uncertain future in court. Though Mr. Trump’s emergency declaration flunks the common-sense test, it might actually pass legal muster, because the relevant law — the National Emergencies Act of 1976 — includes no definition of “emergency,” and courts might be loath to second-guess this president for fear of limiting the discretion of future ones.

What’s more, Congress has already provided a means of checking executive overreach, in the aforementioned National Emergencies Act, through the termination of a declared emergency by a simple majority vote of both chambers. If the Democratic House disapproved Mr. Trump’s declaration, the Senate would be required to vote on the matter, too, within 18 days. Crucially, such a resolution would be considered “privileged” and could not be filibustered.

Democratic leaders in both the House and Senate have pledged to oppose Mr. Trump’s declaration “using every remedy available,” and they should certainly use this one — despite the fact that it comes with a huge disadvantage: Mr. Trump retains the power to veto a joint resolution. Therefore, Congress could terminate the emergency only by overriding his veto, with a two-thirds vote of both houses.

As much of a long shot as this may seem, Congress must pursue a joint resolution for two reasons. First, it is the remedy for executive overreach prescribed by law. And who knows? Eight Republican senators have said they oppose the emergency declaration; a number of others, as well as GOP House members, have expressed misgivings. After a debate in which the full negative implications are made clear — including, for them, the political repercussions and the precedent set for future presidents — it’s just barely conceivable a presidential veto could be overridden.

But only barely — which brings us to the second reason Democrats should use their control of the House to initiate a joint resolution of disapproval: No one in the House or Senate should be allowed to avoid voting on this presidential power grab, and being held accountable for it by the voters. Legal scholars may disagree, legitimately, as to the proper role for judges in protecting legislative prerogatives against alleged executive usurpation. Surely, though, members of Congress should have to stand up and be counted.