It seems President Donald Trump is preparing to claim that some "emergency" on the U.S. southern border authorizes him to act, without new legislation, to spend money and build a wall. Under the Constitution, presidents have no such emergency power. This has been well-established and accepted since at least 1952.

Sixty-seven years ago, President Harry S. Truman acted, without congressional authorization, to seize and run the nation's steel mills. Steel companies and steelworkers had failed to reach a new contract, so a strike was imminent.

Truman, a decent man, believed sincerely that a strike this would harm national security by halting steel production essential to keep arming U.S. forces fighting in Korea and to build nuclear weapons in the Cold War arms race with the Soviet Union. Truman thus declared that, in this "emergency," he had inherent power under the Constitution to take over and run the steel mills.

The steel companies took Truman to court, arguing he had no constitutional power to seize — to steal, if I may — private property. In the Supreme Court, the steel companies won — presidential "stealing" lost — by a vote of 6 to 3.

Justice Hugo Black's opinion for the court declared Truman's action to be unconstitutional. The seizure order amounted to lawmaking, Black wrote, and "the Founders of this Nation entrusted the lawmaking power to the Congress alone in both good and bad times." Justice Robert Jackson both joined in Black's opinion for the court and wrote his own concurring opinion. Jackson's opinion, recognized by subsequent Supreme Courts, including today's, as the central meaning of the steel seizure decision (Youngstown Sheet & Tube Co. vs. Sawyer), is an eloquent landmark in our constitutional law.

Jackson engaged directly and rejected Truman's claim that presidents have emergency powers under the Constitution. "It is something the forefathers omitted" when they wrote the Constitution, Jackson stated. "They knew what emergencies were, knew the pressures they engender for authoritative action, knew, too, how they afford a ready pretext for usurpation. We may also suspect that they suspected that emergency powers would tend to kindle emergencies. Aside from suspension of the privilege of the writ of habeas corpus in time of rebellion or invasion, when the public safety may require it, they made no express provision for exercise of extraordinary authority because of a crisis. I do not think we rightfully may so amend their work .… ."

Today, the matter might be more complicated. The Constitution has not changed — presidents still lack constitutional power to act on their own to identify and then respond to emergencies. But Congress has constitutional power to confer emergency powers on presidents. And since 1952, various Congresses have exercised that power, passing emergency-power bills that presidents have signed into law.

These laws, which authorize presidential declarations of emergencies, are on the books today. Perhaps Trump might claim tonight that one or more authorize him to declare a border emergency and, in some way of responding to that, to order executive branch employees (presumably military personnel) to build a wall.

If Trump claims and attempts to act upon such statutory authority, one recourse would be for Congress to rescind the authority — a disagreeing House and then a disagreeing Senate could pass a new bill repealing whatever emergency-power laws the president was using. But Trump, stuck to his wished-for wall, would likely decline to sign such a repeal bill and instead veto it.

A presidential veto need not be the final act in such a saga, however. More members of Congress could — and in the circumstances as now imagined, should — join and increase the majorities that voted to repeal the emergency authorities in the first place. Such a Congress would be acting on the wisdom to which Jackson alluded in his opinion in the steel seizure case: "A crisis that challenges the President equally, or perhaps primarily, challenges Congress. If not good law, there was worldly wisdom in the maxim attributed to Napoleon that 'The tools belong to the man who can use them.' [The Supreme Court] may say that power to legislate for emergencies belongs in the hands of Congress, but only Congress itself can prevent power from slipping through its fingers."

John Q. Barrett is a constitutional law professor at St. John's University in New York, the Elizabeth S. Lenna Fellow at the Robert H. Jackson Center in Jamestown, New York, and a Jackson biographer. He wrote this article for the Washington Post.