John McCain's campaign accused Barack Obama on Thursday of playing racial politics after the Democratic presidential candidate predicted Republicans would try to scare voters by pointing out "he doesn't look like all those other presidents on the dollar bills."
The exchange marked the most explicit clash on race in the US presidential campaign since Obama became the first African-American to win a major party's nomination. Race has been a sensitive issue for Obama, who is overwhelmingly popular with black voters, but has found it difficult to sway some of his party's white working-class base.
Obama argued on Wednesday that President George W Bush and McCain will resort to scare tactics to maintain their hold on the White House because they have little else to offer voters.
"Nobody thinks that Bush and McCain have a real answer to the challenges we face. So what they're going to try to do is make you scared of me," Obama said. "You know, 'he's not patriotic enough, he's got a funny name,' you know, 'he doesn't look like all those other presidents on the dollar bills."
On Thursday, McCain's campaign accused Obama of using remarks that are "divisive, negative, shameful and wrong."
Obama "played the race card, and he played it from the bottom of the deck," McCain campaign manager Rick Davis said in a statement.
Obama often makes references to his distinctions as a candidate, such as saying there are doubts among some voters because he has "a funny name." At times he refers to his race as well, saying he looks different from any previous candidate but then adding that the differences are not just about race.
In his remarks on Wednesday, Obama did not specify what he thinks a comparison with presidents on US bills would imply - though the currency features older, white men.
Obama spokesman Robert Gibbs said on Thursday that the senator was not referring to race.
"What Barack Obama was talking about was that he didn't get here after spending decades in Washington," Gibbs said. "There is nothing more to this than the fact that he was describing that he was new to the political scene."
Obama has not shied away from describing himself physically. Speaking to 200,000 people in Berlin, he said, "I know that I don't look like the Americans who've previously spoken in this great city," alluding to former presidents John F Kennedy and Ronald Reagan who gave historic speeches there.
And addressing supporters Tuesday at a fundraiser, he said, "It's a leap, electing a 46-year-old black guy named Barack Obama."
McCain has not raised Obama's race as an issue in the campaign; he has said Obama lacks experience.