Ryan appears twice on the ballot in parts of southeastern Wisconsin, both for reelection to Congress from the Republican-leaning district and for vice president. 

If he and GOP presidential nominee Mitt Romney prevail, there will be a special election to fill his seat. If not, assuming he defeats Democrat Rob Zerban, he'll return to the House next year. 

The situation is similar to that Sen. Joe Lieberman (I-Conn.) faced in 2000, when he won reelection to the Senate as a Democrat but he and then-Vice President Al GoreAl GoreOvernight Energy: Exxon sues feds over M fine | Deputy Interior pick advances | Oil concerns hold up Russia sanctions push Gore: Progressive ideas 'gaining ground' among Democrats Gore: Trump prompting 'biggest upsurge' of climate activism ever MORE lost the presidential campaign.

The congressman is heading home Monday night for a get-out-the-vote rally in Milwaukee, and after voting Tuesday morning will fly to Boston to be at Romney's campaign headquarters to watch election results.