Republican John McCain, trailing in polls and searching for a way to gain ground, assailed Democratic rival Barack Obama on Friday in a sharply worded TV ad that said: "When convenient, he worked with terrorist Bill Ayers. When discovered, he lied."

At the same time, McCain moved to restrain the anger that has emerged from some of his crowds this week, telling a town hall meeting in Minnesota that Obama is a "person that you do not have to be scared of as president of the United States."

McCain's new ad is his toughest one yet. It uses Obama's association with Ayers, a Chicago college professor who was an anti-Vietnam war radical in the 1960s, to assert that Obama has "blind ambition" and "bad judgment," and, thus, can't be trusted during an economic catastrophe. "In crisis, we need leadership" _ the ad says and implies that Obama doesn't offer any.

With little more than three weeks before the election, the GOP presidential candidate is seeking to turn his campaign around by steadily escalating his attacks on his Democratic foe and raising questions about his associations with Ayers, who in 1969 helped found the violent Weather Underground group blamed for bombing government buildings in the early 1970s.

But at a Lakeville, Minn., town hall meeting, McCain said his differences with Obama are over "rhetoric and record," not character, and he was booed by his own supporters when he said: "I have to tell you, he is a decent person and a person that you do not have to be scared of as president of the United States."

"I don't mean that has to reduce your ferocity," he said. "I just mean to say you have to be respectful." The comments followed several GOP rallies this week during which angry supporters shouted "traitor," "terrorist," "treason," "liar," and even "off with his head" in reference to Obama.

The Associated Press and other news organizations have reported that Obama and Ayers are not close but that they live in the same Chicago neighborhood and worked together on two nonprofit organization boards from the mid-1990s to 2002. Ayers also hosted a small meet-the-candidate event for Obama in 1995 as he first ran for the state Senate.

During the campaign, Obama has denounced Ayers' radical actions and views.

In a Democratic primary debate in April, Obama called Ayers "a guy who lives in my neighborhood, who's a professor of English in Chicago, who I know and who I have not received some official endorsement from. He's not somebody who I exchange ideas from on a regular basis."

To back up its claim that Obama lied about his relationship, McCain's campaign juxtaposed that debate comment with a CNN report in which a reporter asserted that "the relationship between Obama and Ayers went much deeper, ran much longer, and was much more political than Obama said."

But McCain's campaign provided no other evidence that Obama "lied."

In an interview with Philadelphia-based radio talk show host Michael Smerconish, Obama said Thursday that when he met Ayers in the mid-1990s Ayers was teaching education the University of Illinois. "I was sitting on this board with a whole bunch of conservative businessmen and civic leaders and he was one of the people who was on this board," Obama said of the Annenberg Challenge, a nonprofit educational group. "Ultimately I ended up learning about the fact that he had engaged in this reprehensible act 40 years ago, but I was eight years old at the time and I assumed that he had been rehabilitated."

In response, McCain campaign spokesman Tucker Bounds asked: "Does Barack Obama continue to believe William Ayers has been 'rehabilitated'? Or has Barack Obama changed his mind now that William Ayers is a liability, rather than an asset, to his political ambition?" Continued...