Palin's reference was to Bill Ayers, one of the founders of the group the Weather Underground. Its members were blamed for several bombings, including a pipe bomb in San Francisco that killed a police officer and injured another. Obama, who was a child when the group was active, has denounced Ayers' radical views and activities.
While it is known that Obama and Ayers live in the same Chicago neighborhood, served on a charity board together and had a fleeting political connection, there is no evidence that they ever palled around. And it's simply wrong to suggest that they were associated while Ayers was committing terrorist acts.
Nonetheless, Palin made the comments at three appearances in separate states.
"Our opponent ... is someone who sees America, it seems, as being so imperfect, imperfect enough, that he's palling around with terrorists who would target their own country," said told donors at a private airport in Englewood, Colo. Palin echoed the line later in Carson, Calif., and Costa Mesa, Calif.
Falling behind Obama in polls, the Republican campaign plans to make attacks on Obama's character a centerpiece of candidate John McCain's message in the final weeks of the presidential race. Coming late in the campaign, Palin's remark could be particularly incendiary, either backfiring on McCain or knocking Obama off his focus on the troubled economy — or both.
The campaign was clearly prepared to raise the Ayers' connection to Obama. In addition to Palin's comments at her appearances Saturday, the McCain campaign distributed Palin's comments to reporters.
"This is not a man who sees America like you and I see America," Palin said. "We see America as a force of good in this world. We see an America of exceptionalism."
The Obama campaign called Palin's remarks offensive but not surprising in light of news stories detailing the campaign's come-from-behind offensive.
"What's clear is that John McCain and Sarah Palin would rather spend their time tearing down Barack Obama than laying out a plan to build up our economy," Obama campaign spokesman Hari Sevugan said in a statement.
'The gloves are off, the heels are on'
Palin's remarks come as emails circulate on the Internet with suggestions that the Democratic candidate is secretly a radical, foreign-born Muslim with designs against the US. Obama is a native of Hawaii who lived in Indonesia as boy. He is a Christian.
Palin, Alaska's governor, said that donors on a greeting line had encouraged her and McCain to get tougher on Obama. She said an aide then advised her, "Sarah, the gloves are off, the heels are on, go get to them."
The escalated effort to attack Obama's character dovetails with TV ads by outside groups questioning Obama's ties to Ayers, convicted former Obama fundraiser Antoin "Tony" Rezko and Obama's former pastor, the Rev. Jeremiah Wright.
Ayers is a professor at the University of Illinois at Chicago. He and Obama live in Chicago's Hyde Park neighborhood and served together on the board of the Woods Fund, a Chicago-based charity that develops community groups to help the poor. Obama left the board in December 2002.
Obama was the first chairman of the Chicago Annenberg Challenge, a school-reform group of which Ayers was a founder. Ayers also held a meet-the-candidate event at his home for Obama when Obama first ran for office in the mid-1990s.
In an interview with CBS News earlier in the week, Palin didn't name any newspapers or magazines that shaped her view of the world. On Saturday, she cited a New York Times story that detailed Obama's relationship with Ayers.
Summing up its findings, the Times wrote: "A review of records of the schools project and interviews with a dozen people who know both men, suggest that Mr. Obama, 47, has played down his contacts with Mr. Ayers, 63. But the two men do not appear to have been close. Nor has Mr. Obama ever expressed sympathy for the radical views and actions of Mr. Ayers, whom he has called 'somebody who engaged in detestable acts 40 years ago, when I was 8.'"
Earlier Saturday, Palin spent 35 minutes at a diner in Greenwood Village where she met with Blue Star Moms, a support group of families whose sons or daughters are serving in the armed forces. Reporters were allowed in the diner for less than five minutes before being ushered out by the campaign.
Palin, whose 19-year-old son, Track, deployed last month as a private with an Army combat team, was overheard at one point commiserating with one of the mothers: "Any time I ask my son how he's doing, he says, 'Mom, I'm in the Army now.'"