The only relevant difference is in the doctrine used to assert immunity. With federal courts, the doctrine is that of the separation of powers: each branch is co-equal. With state courts, the doctrine is that of federalism: sovereignty is shared between the states and the federal government.
The concern with federalism is very similar to the concern with co-equal branches. Are we going to leave the door open for states to threaten the President with civil contempt unless he cooperates with their agendas? What if the states serve the president with good-faith process, but the time it would take to comply would prevent the President from doing his job? Or, what if the public nature of open investigations into the President prevents the President from being an effective international diplomat, or from securing cooperation from the Congress? Do you realize that President Clinton and Newt Gingrich were one week away from announcing Social Security reforms before the Lewinsky scandal broke?
Another major difference is that the Vance case is criminal, not civil.
Public perception affects the performance of the President’s duties, especially when it comes to his interactions with Congress. Also, the President needs to review the subpoenas to assert any rights he may have. You don’t pay an accounting firm to fight subpoenas tooth and nail, you pay them to do your taxes. The accountant is supposed to tell you when your records have been subpoenaed, and then it is on you, not them, to fight it out in court. See for example where Mazars refuses to participate in the case at all: https://www.supremecourt.gov/DocketPDF/19/19-635/131128/20200205163042112_Untitled.PDF
Then it’s not really a subpoena, is it? There would be no force behind the order.
Neither do I. One can still have an investigation without compulsory process, the immunity only lasts until the President is out of office, and the limitations period, if there is one, would be tolled until that time.
Did Bill Clinton commit perjury? He was acquitted. How many debates do you want to roll up in this?
Don’t be silly, I don’t think federal prosecutors can investigate a sitting U.S. President for federal crimes, either.
~Max