Madonna has always reveled in controversy and with the recent launch of her concert tour, "Sticky & Sweet," the 50-year-old pop star has kicked up a new fuss by comparing John McCain to Adolf Hitler in a video.

The dust-up is the latest in a career of risky moves that have paid off handsomely for Madonna, whose tours and albums have long mixed music with politics, sex and religion. While other stars rose to fame in the 1980s then faded away, "Material Girl" Madonna has become a global star and even courted controversy to stay relevant to younger audiences.

"Madonna seems to be an extraordinarily brilliant business woman in the business of culture," said Robert Thompson, a professor of media at and pop culture at Syracuse University.

"She's controlled her controversy, so every time she's been in controversy it does her good not bad," he told Reuters.

As her world tour opened in Cardiff, Wales, over the weekend, Madonna showed a video montage juxtaposing images of Hitler with McCain, the Republican senator from Arizona running for president against Democratic Sen. Barack Obama. The Democrats on Monday launched their nominating convention.

McCain's campaign blasted Madonna with a campaign spokesman telling media organizations that the video was "outrageous, unacceptable and crudely divisive."

Abraham Foxman, national director for Jewish group The Anti-Defamation League also issued a statement calling it "outrageous to invoke Nazi imagery in the context of John McCain's candidacy."

In 2005, Rabbis criticized Madonna over a song, "Isaac," that they said used an inappropriate reference to a 16th century mystic. Madonna also has drawn the ire of the Vatican over sexual themes such as simulating masturbation on stage.

Her 1989 song "Like A Prayer," with links between religion and eroticism, caused Pepsi-Cola to cancel a sponsorship deal.

In 1992, she released a book called "Sex" with nude pictures of the star that caused a media sensation, and in 2003 her same-sex kiss with Britney Spears at MTV's Video Music Awards proved to be yet another celebrity news firestorm.

While Thompson noted that Madonna has successfully boosted her career in the past with controversy, he added that celebrities should speak their minds if they want.

"The whole notion of a democratic republic is that this wasn't just about politicians, that anyone could shoot their mouth off about whatever they wanted to," Thompson said.

But David Horowitz, a conservative writer and activist, took a more dim view of Madonna's latest controversy.

"We're in a sad situation if we're turning to entertainers for political wisdom," he told Reuters.

Source: Reuters