In February 2019, Mr. Trump declared that “unlawful migration” at the southern border was a national emergency. At the time, official statistics showed that illegal border crossings were hovering near historic lows. Moreover, Mr. Trump freely admitted that the purpose of using an emergency declaration was to get around Congress, which had refused to fund his pet project, a wall along the border between the United States and Mexico. His administration then announced that it would use emergency powers to raid funding from 127 military construction projects, including ones for weapons maintenance shops, crash fire rescue stations and cyberoperations facilities.

When Congress passed the Emergencies Act in 1976, it included a critical check against just such abuses. Congress would be able to terminate any emergency using a so-called legislative veto, a law that takes effect without the president’s signature. But in 1983, the Supreme Court held that legislative vetoes are unconstitutional, and Congress was forced to amend the law. As it now stands, lawmakers effectively have to muster a veto-proof supermajority to end an emergency. Before last March, Congress had never even attempted such a vote, even though presidents had issued 59 emergency declarations since the law went into effect.

It is proof of the unpopularity of Mr. Trump’s declaration that Congress voted, not once but twice, to terminate the border emergency. In the Senate, 12 Republicans broke ranks to register their disapproval — an extraordinary showing given the party’s record of fealty to Mr. Trump. To achieve a veto-proof supermajority, though, 20 Republicans would have had to defy the president on something that he had made a centerpiece of his presidential campaign. The result was predictable: Mr. Trump twice issued a veto, and Congress was unable to override it.

That left the courts as the sole institutional backstop. To date, federal judges have issued rulings in three cases holding the president’s actions unlawful. Other lawsuits, however, have been thrown out based on findings that the plaintiffs had no right to sue. Mr. Trump, meanwhile, has won the right to continue dipping into the funds while the government appeals the adverse rulings — and has built 101 miles of new border wall.

Lawmakers from both parties have recognized that the system isn’t working. Last July, the Senate Homeland Security Committee voted 12-2 to pass the Article One Act, introduced by Mike Lee, Republican of Utah. Under this bill, presidentially declared emergencies would generally terminate after 30 days unless Congress voted to approve them. This would give the president flexibility when he most needs it — in the moment of crisis — but would ensure that Congress could meaningfully weigh in once the dust cleared. The legislation has broad bipartisan support, as the 2020 presidential election looms and each party considers how these powers might be used if the other side wins. But the bill, like all other legislation, was moved to the back burner during the impeachment proceedings.