Since Marbury v. Madison, judicial review has been a bedrock principle of American constitutional jurisprudence. Some don’t care for it, given that it presents a limitation on the authority of the president to do whatever he pleases, and yet it has served this nation well. You would think a Yale Law grad would recognize this, even if it meant he had nothing to say in defense of his boss whose knowledge and grasp of law, governance and Constitution ranged from none to none. You would be wrong.

This is a very tricky twit by someone who has shed his hillbilly origins and, a la Ted Cruz, backed a pissant who would normalize hate toward Vance’s wife.
If a judge tried to tell a general how to conduct a military operation, that would be illegal.
As with most things legal, the correct answer is “it depends.” If the general’s conduct involved torture, was in violation of a treaty or lacked authority such as a general deciding on his own to bomb Paris, it would very likely be a proper exercise of judicial authority to “tell a general.” Even if not, it would not be illegal, meaning in violation of law, but ultra vires, meaning in excess of his authority.
If a judge tried to command the attorney general in how to use her discretion as a prosecutor, that’s also illegal.
This depends as well. If the exercise of discretion, a prosecutorial prerogative generally, was used in an unlawful fashion, say to prosecute or not based on race, a judge would most assuredly have a say in the attorney general’s exercise of discretion. Judges have a duty to assure compliance with the Constitution (even if that duty is observed mostly in the breach), so if the attorney general uses her authority in a manner that violates the Constitution, a judge has a role to play. To fashion it as a “command” is peculiar, just as call it illegal is the wrong word, but it’s unlikely that Vance’s followers will be troubled by his word choice.
Judges aren’t allowed to control the executive’s legitimate power.
And Vance finally gets to the point of his twit, that neither Judge Engelemayor nor any of the other judges enjoining President Musk’s actions are “allowed” to stop Trump from exercising his “legitimate” power. Vance’s inclusion of the word “legitimate” might seem to provide the necessary squishiness to salvage his otherwise nonsensical assertion. After all, if the exercise of power is legitimate, what possible basis could a judge have to control it?
The problem arises from the determination of what constitutes “legitimate” power and who gets to decide. That authority resides in the judiciary. Remember that old Marbury case, where President Andrew Jackson is reputed to have said, “Marshall has made his decision. Now let him enforce it”?
When the issue before the court is whether the executive has the lawful authority to do something, it is very much in the judge’s control. That’s why they build courthouses. Perhaps the judge’s temporary restraining order will be vacated upon the hearing of the cause. Perhaps the executive will ultimately be vindicated, his authority approved whether by trial or appeal. Perhaps not.
But when a challenge is brought before a judge to the president’s, or his money-buddy’s, authority to take certain actions, the only constitutional response is defend and, should the executive lose, appeal. There is no constitutional option to defy the order of a court, no matter how much you disagree with it or how wrong you believe it to be, under our constitutional order.
Vance calling Musk’s burning down the house a “legitimate” exercise of executive power serves only one purpose, to inflame the groundlings who might be deluded by bad reasoning and inapt analogies, who would then brashly call for their beloved to pull an Andrew Jackson, but this time for real. After all, if it’s illegal, is there not a patriotic duty to fight against this illegality, much as there was a patriotic duty to fight against the stealing of an election four years ago?