Asking because Trump is citing this now while trying to keep documents from being released to the January 6 Commission and prevent his former aides from being subpoenaed to testify.
Sounds like nonsense to me. The Justice Department has also hinted of this continues they'll being charges against aides who refuse subpoenas.
The one assertion that sticks out the most to me in all of this is the one that relates to Bannon. Trump is claiming that his privilege somehow extends to a random person who wasn't even an employee of the executive branch at the time, an approach which no previous President has even attempted to assert, let alone an approach that any court has ever actually upheld. Not to mention, privilege doesn't allow somebody to blatantly defy a subpoena, an action by virtue of which Bannon has committed a crime by engaging in. For sure, Bannon could attempt to assert privilege in order to refuse to answer specific questions or hand particular documents over, an attempted assertion that could then be ultimately resolved through litigation, but Bannon's current stance on the matter is just straight-up opening himself up to criminal liability.
This is the first I've heard of an ex-President invoking it. I suspect that it might be an untested area of the law, which worries me given the current SCOTUS.
Nixon asserted it in response to the Presidential Recordings & Materials Preservation Act of 1974 that ordered the GSA to seize his papers & tapes, thereby resulting in 1977's
Nixon v. GSA, in which the Court held that former Presidents can
assert privilege, but all that that means is that a former President can merely be heard in court on the matter, with it certainly not meaning that such a former President's claims would &/or should then succeed in court. Ultimately, current precedent dictates that privilege is something that belongs to the
presidency as an institution rather than any one President as an individual, hence why it's an incumbent President who ultimately has the final pre-court say on invocations. (Incidentally, everything from "former Presidents" on is the answer to OP's question: potentially, subject to court rulings.)
The Democrats here though are likely going to do what they should have done the first time with Trump's first impeachment trial. Someone is not going to comply with a congressional subpoena: that's contempt of Congress and have them arrested.
The reason that they didn't send criminal referrals of contempt to DoJ in 2019 was because they would've been meaninglessly toothless with Barr as A.G. at the time. Sure, they could've still done so, but his DoJ would've just told Congress to f**k off. This time, however, that's obviously not a problem since Garland is now A.G., which is why you're seeing the likes of Patel, Meadows, & even Scavino engage with the Jan. 6th committee in good-faith - even though Trump begged them not to do so - because they're rational & obviously don't wanna open themselves up to criminal liability. As for Bannon & his blatant refusal to engage with the committee by complying with his subpoena, he should frankly be sh*tting his pants, unless he's intent on becoming some sort of Trumpist martyr or something like that, but even then, he doesn't seem like the type of guy to martyr himself like that, given that he's clearly scared of prison on account of his ultimately-successful begging of Trump for a pardon earlier this year, so his actions right now are making precisely 0 sense insofar as he's once again opening himself to criminal liability, even though he knows full well that the only reason that he got off last time was because he had a pardoning ally in the Oval Office, which is obviously no longer the case this time.