Why no more Catholics in the White House?

[12th Doctor]

Palin is Catholic.

She left the Church.

From what I understand you can't leave unless you're excommunicated.

how does one go about doing that anyway?

Eh, you have to do a bunch of inappropriate things and get noticed doing them. 

Actually there are actions that the RCC considers to cause a sort of automatic excommunication, one being "apostasy, heresy, and schism", which basically just means renouncing the authority of the Pope or "infallible" Catholic doctrine. Which Palin and every other Catholic-turned-Protestant has done. So if you no longer consider yourself Catholic and refuse to practice or recognize Catholic doctrine and the Pope's authority, you've basically excommunicated yourself (making the practice ag speaks of kind of pointless, but these are people clearly just trying to make a political statement.)

Well, I guess technically you have excommunicated yourself but some people within the Church leadership will still say that you a member of the Church until you are officially excommunicated.

You are both correct.