Guilt by association
Obama ties McCain to Bush (6:45), saying "Senator McCain voted for 4 out of 5 of President Bush's budgets"
McCain calls him on it (video 2, 0:15), famously saying "I am not President Bush."
Obama parries (2:50), saying, "If I occasionally mistake you with President Bush...it is because you have been a vigorous supporter of President Bush."
Commentary: Both candidates employed guilt by association at other points in the campaign: the McCain campaign played up Obama's association with former domestic terrorist Bill Ayers and the outspoken Reverend Jeremiah Wright and the less-than-ethical group ACORN. The Obama campaign produced a video that played up McCain's association with savings and loan shark Charles Keating.
One could argue that some forms of guilt by association are valid while others are not. So was Obama's associating McCain with Bush valid? Possibly yes, possibly no. If McCain voted with Bush 90% of the time because he believed that the policies were the best course, then it is indicative of the types of policies he may enact. If McCain voted instead for more political purposes, there is reason to believe that his policies would be different from Bush.
Poisoning the Well
(a satirical example by McCain, which he sets up Obama's coming speech as the "final test of this campaign," 1:10, so that anything Obama says is a letdown)
(Below is a complex example in which Obama brings up McCain's attacks but then says he doesn't want to focus on attacks. It's basically like saying "I don't want you to think about elephants. Don't think about elephants." That forces us getting to think about elephants while disavowing motives.)