Even at 50, the queen of pop just can’t stop courting controversy.

As Madonna kicked off her international “Sticky and Sweet” tour Saturday night, she took a none-too-subtle swipe at the presumptive Republican nominee for president.

Amid a four-act show at Cardiff’s packed Millennium Stadium, a video interlude carried images of destruction, global warming, Adolf Hitler, Zimbabwe’s authoritarian President Mugabe — and Senator McCain. Another sequence, shown later, pictured slain Beatle John Lennon, followed by climate activist Vice President Gore, Mahatma Gandhi, and, finally, Mr. McCain’s Democratic rival, Senator Obama.

The rest of the show had the usual Madonna fixtures: sequins, fishnets, and bondage-style outfits drawn from the 3,500 items of clothing reportedly whipped together by 36 designers specifically for the tour. Dancers sauntered across the stage in top hats and tailcoats, and Madonna tried her hand at break-dancing and pole-dancing.

Some 40,000 fans — many in pink cowboy hats and boas — were treated to a heavy-metal version of “Borderline,” while “La Isla Bonita” served as the backdrop for a flamenco routine. The show, billed as a musical mishmash of “gangsta pimp,” Romanian folk, rave, and dance — was an homage to Madonna’s continuous reinventions over the past three decades.

She exhibited a playful take on her variegated career, mocking dancers dressed as her previous incarnations — including the “Material Girl” and “Blonde Ambition” — before they sank into the stage to the tune of “She’s Not Me.” Madonna finished off the concert with her thumping “Give It 2 Me,” from her new urban-inspired album, “Hard Candy.”

If the world’s top-selling female recording artist is still writhing, shaking, and shimmying with the best of them, her personal life has recently been unsettled. Earlier this summer, her brother Christopher Ciccone published a gossipy memoir, and she has faced speculation about her relationship with New York Yankee slugger Alex Rodriguez and rumors that her marriage to British filmmaker Guy Ritchie is on the rocks — which she hotly denies.

Following Cardiff’s opening concert, “Sticky and Sweet” moves across Europe, hitting London’s Wembley Stadium on September 11 and Paris on September 20. From there, it goes to North America in October before wrapping up December 18 in São Paulo, Brazil.

It is Madonna’s first tour since striking a deal with concert promoter Live Nation Inc. worth an estimated $120 million over 10 years. The partnership gives Live Nation a stake of future music and music-related business she generates, including touring, merchandising, and albums. Madonna’s last tour was her 2006 “Confessions” — in which she staged a mock crucifixion only a few miles from the Vatican.