At the end of their term... why the hell not?
In a midterm though... now that would be fun!
Well, if they lost, they'd just stay on as President of course. Yeah, it'd be amusing having the guy who just beat the President in the Senate race trying to defeat his economic program.
Come to think of it, would be an interesting list....Presidents who lost Congressional races to a member of Congress who was still in office while they were President. Bush 41 was President while Bentsen was in the Senate. That's the only one I can think of off the top of my head.
