The X-Files, Season 2

Scully:
So, you started to tell me about walk-ins but I'm not sure if I grasped the finer points.

Mulder:
Well, it, it's kind of a new age religion based on an old idea. That if you, uh, lose hope or despair and want to leave this mortal coil, you become open and vulnerable.

Scully:
To inhabitation by a new spirit.

Mulder:
A new enlightened spirit. According to the literature, Abe Lincoln was a walk-in. And Mikhail Gorbachev and Charles Colson, Nixon's advisor.

Scully:
But not Nixon?

Mulder:
No. Not even they want to claim Nixon.