Can a former president serve on the cabinet of another president?

Question

example: If Obama wins the presidency, could he appoint Bill Clinton to be his Secretary of State?

Answer 1

Yes, Bill Clinton could be a member of Obama's cabinet. The cabinet  serves at the whim of the President. They are appointed by the President and confirmed by the Senate. There aren't any legal or constitutional requirements.  They CAN be impeached however, so I suppose it would be possible for Clinton to be impeached again!  

Answer 2

In theory, yes. Unlikely, though.

Answer 3

It is possible seeing  as former president Taft became a Supreme court justice.