Key battleground states include Florida, Pennsylvania, Ohio, Michigan, Virginia, Missouri, Wisconsin, Minnesota, Colorado, Iowa, Oregon, New Mexico, Nevada, and New Hampshire.
"The three toughest blue states that the Obama folks have to defend are going to be Michigan, Pennsylvania and New Hampshire," Chalian said. "Those are the three targets for the McCain campaign to try to flip red."
Political analysts say many of the key battleground states are repeats from 2004, but there are some new states where either candidate could make a move.
"You still have to look at Ohio, Florida and the three states that flipped between the two parties which would be New Hampshire, Iowa and New Mexico," said Gonzales of the Rothenberg Political Report. "But I think this year some of the newer battlegrounds are Colorado, Nevada, and we could see Michigan come into play."
The Cook Political Report, a respected election handicapper, sees the November election as a toss-up, with McCain currently holding a 240 to 219 electoral vote edge.
"What we're looking at is a very, very narrow group of states with 79 electoral votes up for grabs," Duffy said.
"There are not an infinite number of scenarios, but there are certainly many, many possibilities," she said.
ABC News' Rick Klein and David Chalian contributed reporting.