Can Trump use a "national emergency" to build a border wall? His own words offer clues.

National emergency declarations are designed to be unilateral and immediate. The main constraint on a president who invoked these powers was supposed to be political and not legal.

This is not to say that Trump's emergency declaration to erect the wall that he promised at the US border with Mexico will not be fought by the federal courts. – it is already disputed.

Historically, the courts have shown deference to the discretionary power of leaders in this area. But not always.

When the federal courts determine whether Trump has exceeded his legal authority, they will consider both the authority flowing from the congressional laws and the inherent authority of the president deriving from the Constitution.

A federal court will probably first consider whether the president had the legal power to act and whether he overstepped the boundaries of that power.

Apart from congressional acts, the president can claim the inherent and undisputed constitutional power to declare an emergency and fund the wall along the southern border. A court would then apply a test dating back to a 1952 Supreme Court decision that ended President Harry Truman's attempt to nationalize the steel industry at the height of the Korean War.

In the judgment of Judge Robert Jackson in the case of Youngstown Sheet & Tube Co. v. Sawyer, the president sometimes asserts his independent power without visible concession nor denial of congressional power. In this average "twilight zone", as Jackson has described, "inertia (or) congressional indifference" may justify the president's assertion of power.

On the other hand, if a president acts contrary to the will expressed by Congress, "his power is at its lowest," said the court in the Youngstown case. In this category, the court will maintain the exercise of the exclusive discretion of the president if it determines that the Congress has no control over that particular area. Although the president generally loses in this category of "lowest price", a recent Supreme Court decision on executive power over foreign affairs shows that sometimes, even when the executive acts on the "lowest power" of the he can win.

Because Trump exercises national emergency powers under the words "national emergency", his other words will also be considered by the court as to whether he acted beyond the scope of his authority. His one hour speech in the Rose Garden Friday, stating that the state of national emergency would be a rich source for those other words that could reinforce or undermine his assertion of authority.

At the forefront of any challenge to Trump's statement will be his statement: "I did not need to do that, but I would prefer to do it much faster." Even a revision court inclined to surrender it to the executive branch could punish it for having made a statement so contrary to the notion of state of emergency.

Trump also missed the opportunity to insert words into the record that could have strengthened his emergency powers.

A federal law, for example, allows military construction in the event of a national emergency, provided that it "requires the use of the armed forces" and is "necessary to support such use of the armed forces". Trump, however, did not utter the words "require", "armed" or "forces" once during his long speech.

On the other hand, Trump did say the word "necessary", when he said: "Our soldiers have been fantastic and I thank them and it is very necessary." He also pronounced the word "support" once, but only to say that "Sean Hannity has been a tremendous supporter of what I am doing". Not meeting the literal requirements of a law is the kind of thing that could be noticed by a federal judge – especially a textualist, or less inclined to refer to executive authority.

As pointed out Professor Robert Chesney of the University of Texas Law School in the Lawfare blog, a construction project supporting the use of armed forces could be more of a fortification than a fortification. a slatted fence. Trump could have relied on his unique interpretation of world history and invoked images of the 1930s Maginot Line – France's "impenetrable" fortification, consisting of retractable artillery turrets, railroad tracks and even barracks. The "Wall" Maginot was a huge construction project, designed to deter and defend against a German invasion. Anyway, Germany eventually invaded the city – just bypassing the wall.

Trump did not talk about a "fortification" or another structure that could "support" the armed forces. Even a variant of the word "strong" could have contributed to reinforcing its argument in favor of the "support" of the armed forces, in the language of the law.

A court could also rely on Trump's claim that "last year, 70,000 Americans were killed, at least – I think their numbers are ridiculously low – by drugs, including methamphetamine, heroin and cocaine, Fentanyl ". This could be a national emergency if drug use is an epidemic – as has often been described. But a court might also conclude that a public health emergency is not a situation requiring military construction or support from the armed forces.

Courts have already taken into account the president's impromptu remarks and his tweets about conscience to assess the legality of his actions, especially in cases of travel bans for Muslims. In particular here, where the president asserts such considerable power by saying a few words, his other words must be relevant to determining whether he really believes in his "national crisis situation".