As the presidential race lurches into its final weeks and John McCain struggles to make a dent in Barack Obama's lead in the polls, the tone at his rallies has grown increasingly negative.

The McCain campaign yesterday sought to distance itself from ugly remarks by supporters, with a spokesman emailing reporters to say the camp "does not condone the inappropriate rhetoric" - a reference to shouts of "treason," "terrorist" and "kill him" by audience members at McCain events following mentions of Obama. The Arizona senator himself has yet to directly address the negative comments.

McCain aides alluded to a coming change in tone in interviews on Friday. "We are looking for a very aggressive last 30 days," McCain adviser Greg Strimple told the Washington Post. "We are looking forward to turning a page on this financial crisis and getting back to discussing Mr. Obama's aggressively liberal record and how he will be too risky for Americans."

Obama and the Democrats say the strategy represents a transparent attempt to distract voters from the economy, an issue on which voters give Obama the advantage, with Democrats independent of the Obama campaign characterising it as a ploy to energise voters who harbour racial animosity and fear.

Among other lines of attack, the McCain campaign has insinuated that the Illinois senator is friendly with a 1960s-era radical who collaborated in a series of bombings and is now an education professor in Chicago, William Ayers, and has asked voters to question who Obama is.

At a rally in Waukesha, Wisconsin today, McCain said, "We need to know the full extent of the relationship."

Obama served on a non-profit board with Ayers, who also held a small fundraising event for Obama early in his political career. Obama has said the two are not friendly and are no longer associated in any way, and no evidence has surfaced to the contrary.

When asked in an interview by ABC's Charles Gibson if he thought Obama's relationship with Ayers was a factor in the presidential campaign McCain said "I think it's a factor about Senator Obama's candor and truthfulness with the American people. That's what I think it's about. As I say, I don't care about Mr Ayers who on September 11, 2001 said he wished he'd have bombed more. I don't care about that. I care about him being truthful about his relationship with him. And Americans will care."

But Republicans are aware that it is logically impossible to prove a negative, and McCain has pushed that to his advantage.

"It's now clear that John McCain would rather launch angry, personal attacks than talk about the economy or defend his risky bail-out scheme that hands over billions in taxpayer dollars to the same irresponsible Wall Street banks and lenders that got us into this mess – a scheme that guarantees taxpayers will lose money," Obama spokesman Tommy Vietor said in a statement, referring to a recent McCain economic proposal.

"While Barack Obama ensured that the rescue plan that passed Congress protects taxpayers and homeowners, John McCain's scheme has been panned by experts and observers from across the political spectrum."

At rallies this week in Florida, crowds jeered and taunted members of the news media. One man hurled a racial epithet at a black television crewman, telling him, "Sit down, boy".

Yesterday, for the second time in three days, a speaker at a McCain rally in Pennsylvania referred to Obama's middle name, Hussein, in an effort to cast doubt on his religion and background. Obama is a Christian.

At the same rally, shouts of "terrorist" and "liar" could be heard following references to the Democratic candidate. On Saturday, McCain running mate Sarah Palin sought to link Obama to Ayers. "Kill him!" one man in the crowd shouted, not specifying who.

"We do not condone this inappropriate rhetoric which distracts from the real questions of judgment, character and experience that voters will base their decisions on this November," McCain spokesman Paul Lindsay said yesterday.

However, Democrats maintain that the rhetoric is being used as a fear tactic.

"It is a wink and nod towards the far right wing and it is embarrassing that any mainstream political party in America would still stoop to these lows," said Paul Neaville, a Democratic consultant who worked for Hillary Clinton's campaign. He said the McCain campaign could do more to repudiate those negative remarks.

"It could go to black neighbourhoods and open offices, it could advertise on minority radio—but it chooses not to because part of their core constituency has a problem with minorities who are poor," he said.

Democratic consultant Erick Mullen, an aide to General Wesley Clark's 2004 bid for the Democratic nomination, said the rhetoric emanating from the dais at McCain rallies show McCain is "either a bad leader or a bad liar".

"The McCain/Palin stagecraft has been extremely well controlled since the GOP convention so it's inconceivable to me that McCain has not tacitly approved the vulgarities uttered from the podium," he wrote in an email. "Or Senator McCain cannot control his own junior staff and party operatives."

Meanwhile, President George Bush took the first step toward handing over the keys to the White House to the next president, establishing a committee to facilitate the transition to the next president, whether its Obama or McCain.

The committee, which will consist of top Bush aides, will help the next president determine staffing needs during the transition, coordinate orientations at executive branch agencies and prepare briefing materials for the next president's appointees.

The next president will be sworn in January 20, but considering the state of the US economy he will not have the luxury of resting the roughly three months following the election.

White House spokeswoman Dana Perino said today that Bush's committee will help the next president hit the ground running in January.

"This is especially important as our nation is fighting a war, dealing with a financial crisis and working to protect ourselves from future terrorist attacks," she said.