Ex-Veterans Affairs Secretary is making his case that he didn’t resign, he was fired.

Shulkin said he had not submitted a resignation letter, or planned to, and was only told of Trump’s decision shortly before the Twitter announcement.

Of course, the format of a resignation is immaterial to the act; in particular, letters are the polite, professional way to quit, but they’re not required, not at all.  Too, learning that your boss wants you to leave “shortly before the Twitter announcement” might be impolite, even impolitic, but again, learning the boss’ desire is not required for resigning.  Nor is desiring one to leave the same as firing that one.

The distinction in this context might seem minor, but it actually flows from a very serious legal matter.

The semantics could be relevant to Trump’s ability to name an acting VA secretary to temporarily fill Shulkin’s place. Last week, Trump named Defense Department official Robert Wilkie to the acting position….
Under federal law, a president has wide authority to temporarily fill a federal agency job if someone “dies, resigns, or is otherwise unable to perform the functions and duties of the office.” There is no mention of a president having that authority if the person is fired.

The fact is, Schulkin may have felt considerable pressure to resign, and it’s common to conflate pressured-to-resign with being fired, but the two are not the same.  Especially here.  Cabinet Secretaries are nominated by the President, but they are confirmed by the Senate.  The President cannot fire a Secretary.  He must be impeached.  It may be that Secretaries serve “at the pleasure of the President,” but once confirmed, they serve “at the pleasure of Congress,” also.

Schulkin could have held out for being impeached, but he resigned—under pressure certainly, but voluntarily nonetheless.