On Friday, President Trump declared that the United States is suffering “an invasion of drugs, invasion of gangs, invasion of people, and it’s unacceptable.” In response, he declared a state of emergency that could help him unlock new money to build a border wall — even without new congressional appropriations.

Judging by early returns, it’s possible that the lawsuits spurred by Trump’s action will be more numerous than the invaders. What kinds of challenges do they raise? That varies suit by suit, of course, and may change depending on how the emergency declaration is implemented. But some broad themes are already clear.

1. Many object that the executive branch isn’t supposed to legislate

The first charge against the emergency declaration is that the executive is legislating. Is the president violating the Constitution by bypassing Congress to spend money on purposes lawmakers had rejected, as Democratic leaders contend?

The Supreme Court case raised early and often in this regard is from 1952. In Youngstown Sheet & Tube v. Sawyer, the Supreme Court blocked an executive order by President Harry S. Truman to nationalize the steel industry, thus preventing a labor strike — because, he argued, such a strike would undermine the U.S. war effort in Korea. Justice Hugo Black’s majority opinion held that Congress had not authorized such a seizure of private property and that “the President’s power to see that the laws are faithfully executed refutes the idea that he is to be a lawmaker.” Truman’s order, the justices said, “does not direct that a congressional policy be executed in a manner prescribed by Congress — it directs that a presidential policy be executed in a manner prescribed by the President.”

Justice Robert Jackson’s concurring opinion in Youngstown sought to lay out a three-“zone” framework for gauging the legitimacy of presidential claims to power. In the first zone, the president acts with congressional approval; here, the president’s authority “is at its maximum.” In the second — which Jackson called the “zone of twilight” — the president acts in a sort of vacuum, without Congress rendering any opinion, and judges would have to assess whether his decision was grounded in the Constitution. In the third, the president’s action is “incompatible with the expressed or implied will of Congress,” in which case “his power is at its lowest ebb.”

Many Democrats in Congress are saying the wall falls into that third zone; after all, Congress considered and rejected the president’s request for wall funding. If so, the Youngstown framework suggests the president’s order should be overturned.

But that’s not a slam dunk. As I discussed here in January, the 1976 National Emergencies Act institutionalized a mechanism that gave presidents the discretion to unilaterally declare emergencies. As I noted then, “nothing in the statute says there actually has to be a national emergency — only that the president declare that there is one.” Read this way, the NEA could put the order in Jackson’s first zone (where Congress has provided “preapproval” for Trump’s action) rather than the third (in direct opposition to congressional preferences.)

That was a stronger argument in January. The president’s choice to wait to issue his declaration until after Congress had overtly rejected his plan helps the case for “Zone 3.”

2. How do you define ’emergency’?

Even so, other legal questions remain. It’s true the NEA does not specify what counts as an “emergency.” Courts rightly privilege presidential judgment when filling in vague statutes, especially concerning national security. Still, the dictionary definition of the term suggests an immediacy not matched by the statistical situation on the border or, for that matter, by the president’s own words during his news conference: “I could do the wall over a longer period of time. I didn’t need to do this, but I’d rather do it much faster.”

It’s certainly possible a court could decide that speed and convenience are insufficient rationales for an “emergency” that could trigger the NEA. Further, the present case goes to the spending power — authority the Constitution explicitly grants to Congress — in ways Youngstown did not. Princeton’s Keith Whittington even speculates that some justices could use this case to rein in what conservatives have long considered excessive administrative delegation to the presidency generally.

3. The NEA can be used only if the ’emergency’ involves using the military

And we’re not done yet. The NEA activates a specific section of law governing military construction spending, funding the administration wants to raid for the wall. Law professors have argued that the section is activated only by an emergency that “requires the use of the armed forces,” at which point only construction that is “necessary to support such use of the armed forces” can occur. Others add that the wall simply doesn’t match the statute’s detailed definitions of the kind of projects it allows.

All this is before we get to private lawsuits fighting the eminent domain the government will presumably use to acquire needed land along the border. It is certainly before the political blowback from members of Congress angry about the loss of their favored long-standing military construction projects — both as a result of the national emergency declaration, and if and when the administration redirects another $3.1 billion from not yet fully identified sources. When pork has clashed with presidential definitions of the public good, pork has a good track record.

Will Congress allow the emergency declaration to stand?

The best possibility the president can hope for, then, is a long delay before any actual wall is built. Congress could answer all the legal questions above — and protect its vital power of the purse — by using the NEA’s procedure to rescind the president’s declaration. It might even revisit the NEA itself.

But that would require a veto-proof majority. Although plenty of members of Congress are on record denouncing executive overreach, that record also shows a near perfect negative correlation between legislative outrage and shared party affiliation across the branches.

The Youngstown case speaks to this point, too. “The opinions of judges, no less than executives and publicists,” Jackson wrote, “often suffer the infirmity of confusing the issue of a power’s validity with the cause it is invoked to promote, of confounding the permanent executive office with its temporary occupant.” A key question looms: Does that go for lawmakers as well?

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