WASHINGTON — Weeks after radio personality Rush Limbaugh began airing a parody titled "Barack the Magic Negro," the song about African-American Sen. Barack Obama's popularity with many white voters is drawing fire from critics who say it is racist.

The audio clip features a comedian imitating the singing voice of Rev. Al Sharpton, bemoaning Obama's popularity with whites who will, the lyrics predict, "vote for him and not for me 'cause he's not from da hood."

Obama's campaign called the song "dumb," although a spokesman said the campaign doesn't think anyone is taking the song seriously.

But Limbaugh's critics say the song goes too far — particularly because the piece is spreading on the Internet at a time when Obama faces security concerns fueled in part by racist remarks and threats directed at him.

"We take these things seriously because there's a consistent pattern of them making their way into the mainstream media and then the mainstream consciousness," said Karl Frisch, a spokesman for Media Matters, a nonprofit media watchdog group. "It's important to shoot these things down."

Obama, meanwhile, has been the subject of explicit, angry comments not only in e-mails and letters but in Web postings. Samples of those writings were reviewed by members of Congress last week when they recommended that the Illinois Democrat be given protection by a U.S. Secret Service detail.

The ramped-up security comes as friends of Obama have been expressing concerns about his safety on the presidential campaign trail, partly because of the size of the crowds he is drawing but also because many of the periodic threats against him carry racial overtones.

Sen. Dick Durbin, D-Ill., said last week that he brought his concerns about Obama's safety to Senate leaders, who agreed with the Secret Service and Department of Homeland Security that the presidential hopeful needed a special security detail.

"Unfortunately, many of the things that concerned me had a lot to do with race," Durbin said last week.

"I wish we lived in a country where that is not a problem, but it still is. And the fact that Barack Obama is such a highly visible African-American candidate, I think, increases his vulnerability."

So virulent have been some of the postings on Web sites that last week CBSNews.com told its staff not to enable comments on stories about Obama.

The candidate was drawing an overwhelming number of racist remarks in the postings.

As for Limbaugh and the controversial song, it started in March shortly after the Los Angeles Times published a column by a black writer calling Obama the "Magic Negro."

The article said Obama fits the prototype of the black cinematic figure who arises to "assuage white guilt over the role of slavery and racial segregation in American history."

Columnist David Ehrenstein suggested Obama is running in the public imagination for the office of "Magic Negro" — a kind of benign African-American figure who is there to help and for whom even mild criticisms are waved away "magically."

The term "Magic Negro" in cinematic circles dates to the 1950s.

Not long after that column was published, Limbaugh began to air "Barack the Magic Negro," sung to the tune of "Puff, the Magic Dragon."