SOMETHING POSITIVE has come out of the otherwise troubling situation in which President Trump has managed — so far — to thwart the will of Congress and allocate funds to his proposed border wall. There is an increasing awareness on Capitol Hill that Mr. Trump is taking advantage of past lawmakers’ excessive delegation of power to the executive branch. Whether legislators override Mr. Trump’s veto of their termination of his emergency declaration or — as seems far more likely — fail to override it, the legislative branch needs to take back its legitimate powers.

To review, there are 123 statutes that enable the president to make policy in particular areas without going through ordinary lawmaking processes upon the declaration of a “national emergency,” according to the Brennan Center for Justice. This includes the military construction law Mr. Trump has cited. Overarching them all is the 1976 National Emergencies Act and the 1983 Supreme Court ruling in Immigration and Naturalization Service v. Chadha, which, taken together, created the legal framework today: A president can declare an emergency, and there’s nothing Congress can do to rescind it without a veto-proof majority.

There are many ways Congress could change this. One, suggested by conservative legal scholar Josh Blackman, would be a statute providing that all emergency declarations expire automatically after three months, whereupon the president would have to ask Congress for an extension. Another approach, embodied in a new bill drafted by Sen. Mike Lee (R-Utah), would automatically terminate an emergency declaration within 30 days unless Congress voted to extend it. It would also empower Congress to limit or amend emergency declarations, and impose reporting requirements on the president regarding the exercise of emergency powers. Rep. Andy Biggs (R-Ariz.) is sponsoring a similar measure in the House; Reps. Tom Reed (R-N.Y.) and Josh Gottheimer (D-N.J.) are promoting a 60-day bill.

Mr. Lee’s bill came as part of a last-ditch GOP effort to cobble together something Republican senators could vote for at the same time they approved Mr. Trump’s border emergency — so as to back the president while appearing to rein him in for the future. Democrats understandably opposed the bill in that context; House Speaker Nancy Pelosi (Calif.) said she would not bring it up for a vote, which was superfluous because Mr. Trump rejected the gambit, too. Now, however, the proposal stands on its own and, as such, merits consideration.

In fact, legislation to reform national emergencies would be one way to salvage a measure of good-governance reform from this whole episode. Both parties have an interest in recouping Congress’s legitimate powers; certainly the country has an interest in restoring a robust separation between the legislative and executive branches.