The gloves have well and truly come off in the US presidential race after Sarah Palin accused Barack Obama of associating with terrorists.
The Democrat's campaign team described the comments as "offensive" but said they were not surprising.
Mrs Palin, the Republican vice presidential nominee, made the remarks during a speech to supporters at a fundraiser in Colorado.
She said Obama "is someone who sees America, it seems, as being so imperfect that he's palling around with terrorists who would target their own country".
The Alaska Governor was referring to William Ayers, a member of the radical 1960s group the Weathermen who placed bombs at the Pentagon and the Capitol.
He reportedly supported Mr Obama's first run for public office in 1995.
The Obama campaign described Mrs Palin's guilt-by-association attack as "desperate and false".
Campaign spokesman Hari Sevugan said the accusation was part of the McCain/Palin ticket's newly aggressive "come-from-behind" strategy with only a month left before the vote.
He said:"Governor Palin's comments, while offensive, are not surprising, given the McCain campaign's statement this morning that they would be launching Swiftboat-like attacks in hopes of deflecting attention from the nation's economic ills."
Republicans have promised to ramp up the rhetoric ahead of the November 4 election in a bid to arrest Senator McCain's recent dip in the polls following his role in delays to the $700bn economic bail-out.
On Friday, his top adviser Greg Strimple promised a "very aggressive last 30 days" of campaigning.
"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," he told reporters.
There is a month left, and they (the Republicans) are not doing very well in the polls. They pulled their troops out of Michigan - they are having a difficult time in states that Bush won both in 2000 and 2004 like Virginia, North Carolina, Florida, Colorado. They're getting a little anxious and a little nervous.US political analyst Jon-Christopher Bua
The Democrat nominee has emerged strengthened from the financial crisis, boosting his polling lead to an average of six points over Senator McCain, according to RealClearPolitics.com.
The latest Gallup tracking poll of registered voters puts Mr Obama on 50% and Mr McCain on 42%.