Pablo Monsivais photo
President Barack Obama stands at the heliport overlooking the Hoover Dam, Tuesday, Oct. 2, 2012 in Boulder City, Nev.
Charles Dharapak photo
Republican presidential candidate, former Massachusetts Gov. Mitt Romney greets passers-by as he makes an unscheduled stop at a Chipotle restaurant in Denver, Tuesday, Oct. 2, 2012.
Chuck Burton photo
Vice President Joe Biden speaks during a campaign event in Asheville, N.C., Tuesday, Oct. 2, 2012.