At midnight on April 8, 1952, with U.S. troops mired in a muddy stalemate two years into the Korean War, American steelworkers prepared to go on strike. Talks broke off, mediators resigned, and the companies began to furlough employees. In a television address — one of the first ever — President Harry Truman announced that he was seizing the steel industry and ordering plants to reopen. Federal agents raised an American flag over the mills. The New York Daily News front page blared: TRUMAN DOES A HITLER.

But when the Supreme Court ruled, six justices blocked Truman’s action. Youngstown Sheet & Tube Co. v. Sawyer was among history’s most important decisions. Truman lacked the power to seize the mills, the justices wrote. Presidential power is limited. Notably, every single member of that court had been nominated by Truman or his long-serving Democratic predecessor, Franklin D. Roosevelt. The justices had just lived through World War II and seen the danger of dictatorship and the perils of executive overreach abroad.

Tomorrow, the Supreme Court will hear Learning Resources v. Trump. Today’s justices will consider whether President Trump’s unilateral imposition of massive tariffs — his “Liberation Day” levies that continue to roil the world economy — is legal. Former federal judge Michael McConnell, a prominent conservative, calls it “the most significant case on presidential power since the steel seizure case in 1952.”

Since the beginning of the year, the high court’s members have wriggled and squirmed to avoid directly ruling on Trump’s epic power grabs. This time they will have no choice but to act in public.

Blocking the tariffs would blow a hole in Trump’s signature economic policy. Acquiescence would blow a hole in the Court’s credibility and our constitutional order.

The Constitution gives Congress the power to set tariffs. Congress can delegate aspects of that power to presidents and has done so — but always with conditions and limitations on its exercise. Every court that has ruled on this so far has agreed that Trump’s tax hike by fiat was illegal.

The White House argues that the International Emergency Economic Powers Act and the National Emergencies Act, laws the president can invoke to respond to emergencies, give him the power to set blanket tariffs. But as my colleague Elizabeth Goitein explains, these laws were designed to limit how the president responds to the emergencies, not expand them. And they certainly weren’t meant to authorize the use of emergency powers in a situation where it is clear that no true “emergency” exists. “No president has ever interpreted the statute to authorize tariffs, let alone across-the-board tariffs on imports from friendly nations.”

The Brennan Center filed a friend-of-the-court brief on those emergency powers. It argues, “Allowing the president’s actions to stand could have far-reaching consequences beyond this case. It would give presidents a green light to use emergency powers as a means of evading the authority of Congress.”

George F. Will, the venerable conservative columnist for The Washington Post, wrote a column that cited our brief. Will asked, “For what more momentous controversy might the court be hoarding the prestige that enables it to do its duty to police the excesses of the political branches?”

As Will’s column suggests, alarm extends across ideological lines. Twenty briefs from members of Congress, former government officials, economists, businesses, and groups including the libertarian Cato Institute and the conservative Goldwater Institute joined in. Michael McConnell was so fired up that he joined the legal team challenging the tariffs.

We recall when the Court stood up to Harry Truman. Where will this set of justices come down on this epic test of presidential power?

On the one hand, when Joe Biden was president, the Roberts Court regularly issued ringing pronouncements about executive aggrandizement. Only Congress, the justices announced in 2022, could decide “major questions.” If ever a “question” were “major,” the multitrillion-dollar tariff topic would be one.

And yet the same Roberts Court granted presidents vast, unprecedented, and previously unimagined immunity from criminal prosecution.

Why did Trump barrel ahead with such a broad and illegal approach in the first place? After all, presidents have significant — although not unlimited — tariff-setting powers under existing trade laws. In his first term, Trump raised levies on goods from China numerous times, as did Biden. And if Trump believes that existing laws don’t afford sufficient leeway, he can ask Congress to provide more.

The illegality itself seems to be a point of attraction. It’s part of a concerted effort to bend or dismantle the few checks placed on executive power.

Justice Robert Jackson, who as the U.S. prosecutor at the Nuremberg war crimes trial knew the danger of letting executive power run loose, wrote a famous concurring opinion in the Youngstown Sheet & Tube case.

“With all its defects, delays and inconveniences, men have discovered no technique for long preserving free government except that the Executive be under the law, and that the law be made by parliamentary deliberations,” Jackson wrote. “Such institutions may be destined to pass away. But it is the duty of the Court to be last, not first, to give them up.”