If even one conservative justice entertains the idea that the President cannot be prosecuted for acts done while in office, I would love to see the prosecutor bring up the hypothetical example of a sitting President disagreeing with SCOTUS rulings and sending in Seal team 6 to kill Supreme Court justices who rule against him.

Seems unlikely a conservative justice would entertain a categorical prohibition on Presidents being prosecuted for acts while in office. But I think they will have some pointed questions about whether some acts of a President deserve criminal immunity.

Clearly if Congress passes a law that says a President cannot meet with a foreign head of state without prior Congressional approval, that would violate the Constitution, and the President would ignore it without a moment's thought. Let someone try to bring a challenge to enforce it. But if that law makes a violation a felony, so that the President might walk out of office into a criminal prosecution....well, that might be different story.

The Court is almost certainly not going to be concerned with Presidential acts that are clearly and unambiguously unjustified. They're going to be concerned about Presidential acts that are of a type and nature that the President routinely conducts today, but might theoretically be subject to criminal prosecution - either by deliberate targeting by Congress or (more likely) some of the very broad criminal statutes that a creative prosecutor might bend to suit. No President is going to order a Seal Team 6 assassination thinking that any ruling will immunize them from it. The concern would be that when a President faces a decision whether to ask the DOJ to prioritize fighting fentanyl dealers or white collar crime, or whether to withdraw from a treaty governing money laundering, that when some donor or contributor or whomever is found to have benefited from it that the President might face some amorphous conspiracy charge - so that the President starts second-guessing all their actions that are in spheres that might race that specter.

IOW, if the Court overrules the lower courts, it will not be because they think Seal Team 6 is free for assassinations. It will be because they've decided that the answer on immunity is neither "always nor "never," but "it depends."