Republican John McCain's age and Democrat Barack Obama's thin national resume likely make the candidates' choice of running mates more critical to a November victory than in any presidential election in recent memory. Should McCain win, he would be 72 when he takes the oath of office, the oldest first-term president in US history. He has survived three bouts of melanoma, the most serious form of skin cancer, and acknowledges his choice of a vice presidential running mate will be of “enhanced importance.” The vice president takes over running the country if the president is incapacitated or dies. Obama would be only two-thirds through his first term in the US Senate and had virtually no national exposure before delivering an attention-grabbing and soaring keynote speech at the 2004 Democratic convention. His vice presidential choice could help him overcome voter questions about his lack of experience while showing he would appoint strong figures to his government. “More than in any election I can remember, the vice presidential choices made by these candidates stand to make a significant difference, especially among undecided voters,” says Kenneth Dautrich, professor of public policy at the University of Connecticut. In most presidential races, the vice presidential candidate is largely irrelevant and a majority of those who have held the job were kept busy with ceremonial tasks. George H. W. Bush, who was elected president in 1988 after serving two terms as Ronald Reagan's vice president, attended so many state funerals that he was quoted as having said: “I'm George Bush. You die, I fly.” Since then, however, Al Gore and Dick Cheney, vice presidents respectively for Bill Clinton and George W. Bush, were much more powerful figures. Political scientist Robert Loevy says McCain must “reassure people about his age,” making his vice-presidential selection critical “because of the greater likelihood that person could become president.” The Colorado College political science professor says that Obama's running mate selection is equally important, especially since he would be the first African American US president. – AP __