Subject: Re: Twenty Weeks to Topple a Republic
Under what authority did Obama use to justify drone strikes on U.S. citizens abroad fighting for the enemy? Or Bush's infamous deck of cards with various Iraqi leaders on it?

So how would it be different if Trump gets the White House Counsel to write up on official letterhead that Gavin Newsom (or whomever) is deemed to be a terrorist and enemy of the U.S. due to acts that are not in the interest of the U.S. and that he is to be captured or killed immediately?

Under his authority as Commander in Chief. The President is authorized to use military force against non-citizens abroad, when they pose a military threat to the U.S. There are some very narrow precedents for using military force against U.S. citizens abroad fighting for the enemy.

None of that would apply to Gavin Newsom. If he is a terrorist and an enemy of the U.S., and is located within the U.S., then he is subject to the protections of the Constitution and cannot be the subject of an extrajudicial killing. The President has no authority to do that under his authority as Commander in Chief. The apprehension or neutralization of a U.S. citizen on U.S. soil is a law enforcement matter, not a military matter - you can't just kill them.

I've sort of changed your hypothetical to be a straight up assassination, because I think the scenario you described is one that Trump was probably already immune from. It's not entirely clear that what you're describing is a crime. If Trump orders that Gavin Newsome is to be arrested and taken into custody, it would violate a number of civil statutes (wrongful arrest, malicious prosecution)....but the President is already completely immune from any civil liability for the exercise of his office. And I'm not sure that getting the White House counsel to write up something about Newsom on official letterhead is even that.