On the Trail: Barack Obama, John McCain, Hillary Clinton

Sen. Barack Obama shakes hands with supporters after speaking at a town hall meeting in Greensboro, N.C.  (Alex Brandon / Associated Press)

Democratic presidential hopeful Sen. Barack Obama shakes hands with a young supporter after speaking at a town hall meeting in Greensboro, N.C.  (Alex Brandon / Associated Press)

Democratic presidential hopeful Sen. Hillary Clinton speaks at a fundraising event at the Daughters of the American Revolution Constitution Hall in Washington.  (Nicholas Kamm / AFP/Getty Images)

Supporters of Sen. Hillary Clinton cheer as she speaks at a fundraising in Washington.  (Nicholas Kamm / AFP/Getty Images)

Sen. Hillary Clinton speaks about the economy at Wake Technical Community College in Raleigh, N.C.  (Charles Dharapa / Associated Press)

Republican presidential hopeful Sen. John McCain addresses supporters during the Orange County Hispanic Small Business Roundtable in Santa Ana.  (Joshua Gates Weisberg / EPA)

Republican presidential candidate Sen. John McCain autographs a photograph after a campaign appearance in Orange County.  (Mary Altaffer / Associated Press)