Minnesota Gov. Tim Pawlenty, who supports McCain, criticized Obama's association with William Ayers, whose 1960s group, the Weathermen, committed bombings on the Pentagon, the U.S. Capitol and across the nation.

"Now Barack Obama at the time was 8 or 9 years old, or whatever, but that's not the point, the point is this same individual, Bill Ayers, hosted some sort of political event at his home for Barack Obama when Barack was running for state Legislature in Illinois when he was well into his 30s," Pawlenty said. "It goes to the issue of what kind of judgment would allow an unrepentant domestic terrorist to host a political event for you in his home, in the terrorist's home."

Sen. Sherrod Brown, D-Ohio, an Obama supporter, said what the voters are concerned about is the economy, not negative attacks on a candidate.

"Well, you've seen a 26-year Senate veteran morph into an angry, desperate candidate in the last few weeks, especially in the last few days," Brown said of McCain "And it just kind of makes me sad … that John McCain and Sarah Palin are resorting to these tactics."