I was bored, so I went back and checked.
Just to point out a major difference between Powell and Santo's.
Powell was elected and EXCLUDED from being seated, taking the oath, and functioning as a Representative. That is not the case with Santo's, he has been seated and the action would not be to EXPELL him. "Exclusion" and "Expulsion" are two different things.
In the SCOTUS decision, the limitation mentioned apply to seating a Representative by rejecting the vote of the district. Which, as you pointed out would be a limit on Congress to the Constitutional qualifications to hold office. However Powell appears to be less germane to the Santo's situation since he has been seated and would be expelled. The difference appears to still be open before the court.
So the Constitutional qualification requirements are:
- 25 years of age,
- 7 years a citizen,
- Inhabitant of the State at the time of election
Congress's refusal to seat Powell in 1967 was not based on age, citizenship, or residence and that was the basis the SCOTUS judged on. It would make no sense, to imply those are the only reasons that the Congress can therefore expel a member. It does make since for Congress to have the power to expel a member after being seated for ethics or criminal violations.
WW