[David]

“The de facto officer doctrine confers validity upon acts performed by a person acting under the color of official title even though it is later discovered that the legality of that person’s appointment or election to office is deficient.” Ryder v. United States (94-431), 515 U.S. 177 (1995).

Correct. Nothing to do, however, with eligibility to hold office which is not a deficiency in "legality of appointment or election to office".

[DoodleDawg]

Nothing to do, however, with eligibility to hold office which is not a deficiency in "legality of appointment or election to office".

Then what is it? And what is "deficiency in legality of appointment or election to office?"