March 28, 2008 | On the Trail | Barack Obama, Chelsea Clinton, John McCain

Chelsea Clinton, along with Philadelphia Mayor Michael Nutter, campaigns in the city for her mother, Sen. Hillary Rodham Clinton.  (Matt Rourke / Associated Press)

Democratic presidential hopeful Barack Obama poses with the cast of “The View” during a taping Thursday in New York for Friday’s show. With the Illinois senator, from left, are Whoopi Goldberg, Barbara Walters, Joy Behar, Sherri Shepherd and Elisabeth Hasselbeck.  (Steve Fenn / Associated Press / ABC)

Presumptive Republican nominee John McCain, left, accompanied by his former presidential rival Mitt Romney, speaks at a news conference in Salt Lake City. The two campaigned together in Utah and Colorado.  (Danny La / Getty Images)

Romney campaigned with McCain, his former opponent in the presidential race, in Utah and Colorado.  (Danny La / Getty Images)