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 US president. Amid a four-act show at Cardiff's packed Millennium Stadium, a video interlude carried images of destruction, global warming, Nazi dictator Adolf Hitler, Zimbabwe's authoritarian President Robert Mugabe - and US Senator John McCain. Another sequence, shown later, pictured slain Beatle John Lennon, followed by climate activist Al Gore, Mahatma Gandhi and finally McCain's Democratic rival Barack Obama. Following Cardiff's opening concert, "Sticky and Sweet" moves across Europe, hitting London's Wembley Stadium on Sept. 11 and Paris on Sept. 20. From there, it goes to North America in October before wrapping up Dec. 18 in Sao Paulo, Brazil.