3. The inherent difficulty/sensitivity of running against two figures at once. McCain will have to 1) explicitly criticize a sitting Republican president before Republican audiences and 2) prevent the historic event of electing the nation’s first African-American president that many in the country (and the media) desire.
It occurs to me that there's a relatively painless solution to this problem: don't criticize Bush/Cheney, just criticize Cheney. He's the real lightning rod in the administration, the most powerful vice president in our nation's history.