Possible Clues:

• First vice president to have a Facebook page
• Head of the Senate's Foreign Relations Committee
• Politico with the 2007 autobiography 'Promises to Keep'
• 2008 Palin counterpart
• Former senator known as "Amtrak Joe"
• Veep under Obama
• End of the letter: 'Thanks for the laugh. I'm voting for Obama/__.'
• Ex-senator known as 'Amtrak Joe'
• Senate president
• 11 Down's vice president