President Trump’s decision to declare an emergency so as to be able to build a wall on the Mexican border puts him in a zone of twilight. That’s not a phrase from Rod Serling. It’s from the pen of Justice Robert Jackson of the Supreme Court, concurring in one of the most memorable opinions ever to flutter from the high bench. It defined when a president’s powers are at a peak or nadir.

The case in which Justice Jackson concurred (he was a wonderful constitutional wordsmith, by the way, although he never finished law school) is known as Youngstown Steel v. Sawyer. It was handed down during the Korean War, when the justices blocked President Truman from seizing the steel plants. It was a terrible rebuke for the president (not to mention the free Koreans).

What Justice Jackson’s opinion is famous for is the idea that, as he put it, “presidential powers are not fixed but fluctuate depending upon their disjunction or conjunction with those of Congress.” He sketched what he called a “somewhat over-simplified grouping” of “practical situations in which a President may doubt, or others may challenge” a president’s powers.

A president’s authority is at its “maximum,” Jackson wrote, when he “acts pursuant to an express or implied authorization of Congress.” In the absence of either a congressional grant or denial of authority, Jackson jotted, a president “can only rely upon his own independent powers” — though Jackson added (and this is where he nailed it) there is a “zone of twilight.”

That zone of twilight is precisely where President Trump is plunging in respect of the wall. He made a bright line campaign promise to build the wall. No presidential candidate has ever made a clearer campaign promise. It is, though, different than other stump sweet talk, like, say, the moving our Israel embassy to Jerusalem or withdrawing from the Iran appeasement.

In the case of the Jerusalem embassy and the Iran appeasement, Congress was four-square behind Mr. Trump. Indeed, it was there ahead of him. In the case of moving the embassy, the Congress was almost unanimous. In the case of Iran, both houses of Congress opposed the appeasement “overwhelmingly,” as it was put in an editorial in the New York Times.

The wall on the Mexican border, that’s a different story.
The Congress is not there, at least not at the moment. It was prepared to make a churlish compromise, giving Mr. Trump less than $2 billion and leaving him to tap other funds appropriated for emergencies that the president was left to define. So Mr. Trump is athwart of at least one house of the Congress.

Justice Jackson sketched a third level of president authority, its nadir. That’s when “the President takes measures incompatible with the expressed or implied will of Congress.” Then his power is “at its lowest ebb,” and, he wrote, “Courts can sustain exclusive presidential control in such a case only by disabling the Congress from acting upon the subject.”

Whether Mr. Trump’s maneuver will land him in court and how he would fare, we don’t know. He reportedly plans to use rarely invoked authority, passed by Congress, to tap certain military funds in emergencies. The measures, long on the books, weren’t legislated for the wall. A certain amount of discretion, though, was left to the president. The House is mad as the dickens, and it’s easy to see why.

That doesn’t mean the president is wrong, though. His campaign promise was so blunt, and the states gave him such a mandate in the electoral college, that it’s easy to see why he’s determined to act. As we write this, the budget bill hasn’t been sent over to the White House. Maybe there will be a hangup. Or may the president will sign it and declare the emergency. Rod Serling, call your office.

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Correction: Finished is what Justice Jackson never did in respect of law school. His education was mis-stated in an earlier edition.