Two words. Bill Clinton. He had to testify in the Paula Jones case after a 9-0 SC decision.
The difference is that BJ was under investigation, directly.
In the meantime we get to see judicial malpractice,
and the Paula Jones case was a civil suit versus this one that is criminal.
And Bill Clinton never insulted the court the way Bambi did during his SOTU. Can you imagine the opinions if this were to get to their desks?
There have been a number of sitting US Presidents who have had to testify according to subpoenas. I can’t give you the list off the top of my head, but I know it’s more than just Clinton who has been required to do so.
I may be wrong, but I believe what Clinton was arguing for was that the entire case be suspended until he was out of office, the objection wasn’t simply to having to testify. The Supreme Court ruled that the case could continue, but the specific question of whether a sitting president can be compelled to give testimony in court was never touched on.
Not trying to be pedantic, and certainly not a Clinton-supported by any stretch. But I think the heart of this matter about the subpoena and a president did not actually get addressed back then.