Oct 8, 2008 -- The McCain campaign has made no secret of its plans to spend these final weeks of the election going negative -- attacking Sen. Barack Obama on his judgment, questioning his associations and unleashing self-described "pitbull" Alaska Gov. Sarah Palin to do much of the dirty work.

"For me, the heels are on, the gloves are off," she told a group of Republican donors in Naples, Fla., on Monday.

As the rhetoric at Palin's rallies has ratcheted up, so too has the language of supporters in the crowds coming to see her. At rallies in Florida, supporters were heard yelling "treason" and "traitor" when Obama's name was mentioned.

At a rally on Monday in Clearwater, one man shouted "Kill him," according to the Washington Post, after Palin mentioned Obama's association with 1960s radical Bill Ayers. It was not clear who made the comment or if the man was referring to Ayers or to Obama, but the Secret Service says it will investigate.

"One of [Obama's] earliest supporters is a man named Bill Ayers," she said Monday, eliciting boos from the crowd. "And, according to the New York Times, he was a domestic terrorist and part of a group that, quote, 'launched a campaign of bombings that would target the Pentagon and our U.S. Capitol,'" she said to more boos and the one man's call to "kill him."

Palin's speeches and a series of recently released negative ads, some pundits say, are all par for the course in the waning days of a closely fought contest. Now questions are being raised, by the opposition and by outside observers, about whether Palin is stoking people's worst natures and, more broadly, about when a candidate should take her supporters to task when they go too far.

"At some level, negative rhetoric is part of the game. But is it truly dangerous?" asked Kimberly Gross, a professor of political communication at George Washington University. "Is someone going to kill Barack Obama because they went to a Palin rally? Probably not, and if they do it is more likely because they're crazy than because they heard someone tell them to do it at a Palin rally. It is dangerous in a bigger sense that it is bad for politics."

Making the rounds on today's network morning shows, Democratic vice presidential nominee Joe Biden of Delaware called Palin's attempt to link Obama and Ayers "mildly dangerous," on CBS's The Early Show

On ABC News's "Good Morning America" he said: "This really is a case where when you don't have anything to talk about, attack -- and I think that's really over the edge"

"Some of the stuff she's saying about Obama and some of the stuff people are yelling from the crowd, if she hears it she should be able to say 'Whoa whoa whoa, that's overboard.' This is volatile stuff and I thought we were kind of beyond this place," he said.

Gross said politicians had a responsibility to call out their supporters when they say offensive things, not only for the good of their own electoral chances but for the good of the political system.

"In my opinion candidates have a responsibility to say something," she said. "Negative campaigning per se is not absolutely a bad thing, and can be informative. But candidates do us disservice when they create the conditions that can allow a crowd to get out of hand. It just reinforces a cynicism about politics."

Though much of the negative campaigning has fallen to Palin and the crowds who attend her rallies tend to come from the further right wing of the Rupublican base, McCain had a moment recently in Albuquerque, N.M., when a member of the crowd shouted a smear, which the candidate appeared to hear but said nothing about.

"In short," McCain asked the crowd, "who is the real Barack Obama?"

"A terrorist," yelled someone from the crowd, eliciting a laugh from others in the hall and a perplexed look from McCain, but he continued his speech without comment.

On NBC's "Today" show, Biden called some of the language being used by crowds at Republican rallies "semi-vile" and said Palin should have condemned those who shouted provocative epithets.

"Heard that a couple of people hollering from the audience, you know, semi-vile things about, you know, 'terrorist' and things like that. And the idea that a leading American politician who might be vice president of the United States would not just stop mid-sentence and turn and condemn that, you know, I just -- this is -- this is a slippery slope. This is a place we shouldn't be going," he said.

Calls for comment from the McCain-Palin campaign were not yet returned.

Reporters following McCain and Palin say that crowds have become increasingly hostile towards them, yelling at them as they get off the press bus to cover events. The Palin crowds, they say, are typically more aggressive than those found at McCain-only events, especially since Palin's interview with CBS's Katie Couric in which she appeared to be uninformed on major policy issues.

In Clearwater, reporters were taunted by the crowd of about 3,000 people. Palin blamed Couric for her "less-than-successful interview with kinda mainstream media."

One Palin supporter used a racial slur against an African-American sound technician working with a television crew and told him to, "sit down, boy."