Crowds in Wisconsin and Pennsylvania have repeatedly booed Mr. Obama and yelled “off with his head,” and at a rally in Florida where Ms. Palin appeared without Mr. McCain, The Washington Post reported that a man yelled out “kill him.” At the same rally, a racial insult was hurled at an African-American television cameraman.

Representative Elijah E. Cummings, a Maryland Democrat, said Friday in an interview that he was surprised that neither Mr. McCain nor Ms. Palin had reacted, either by chastising audience members or discussing the events later. “It concerns me greatly when people come to the point where they take a political race, a race for president, and holler out words like ‘kill him,’ ” he said. “I just think our country is so much better than that.”

At the same time, Mr. McCain’s advisers sought to minimize the impact of those images of angry voters that have repeatedly been broadcast on television in the last two days.

“I don’t think it’s that big a deal,” Rick Davis, Mr. McCain’s campaign manager, told reporters in a conference call on Friday. “I think political rallies have always attracted people who have an emotional connection to the outcome of an election.”

Nicolle Wallace, one of Mr. McCain’s senior aides, tried to turn the tables on Mr. Obama on Friday and accuse him of denigrating the people who go to Mr. McCain and Ms. Palin’s rallies. “Broadsides against our supporters are insulting,” she said. “He attacks the same people he once called bitter.”

Within the campaign, there is a difference of opinion on the attacks, and some of Mr. McCain’s closest advisers have felt he should also criticize Mr. Obama for his ties to his former pastor, the Rev. Jeremiah A. Wright Jr. But they say Mr. McCain believes that if he does so, he will be accused of racism.

“I personally believe that Jeremiah Wright is a legitimate issue to bring up,” one of Mr. McCain’s top advisers said. “But the candidate is refusing to do that out of an abundance of caution.”