The McCain camp is betting that undecided voters will "break at the end of the day" for the Republican, Stephanopoulos said.
"That's not what we show. ... We think they'll break pretty evenly for McCain and Obama," he said.
Stephanopoulos said the election could be decided in the early hours of the evening as polls close between 7 p.m. and 8 p.m. in six states: Indiana, Virginia, Ohio, North Carolina, Pennsylvania and Florida.
For McCain to keep his hopes alive, he must win all of the Bush states plus Iowa, Colorado, Nevada and five of those six states, although he is tied or trailing in all of those states in polls the day before the election.
Or, if McCain wins Pennsylvania, McCain could then afford to lose others, but the polls suggest he is 10 points behind in Pennsylvania.
ABC News' Bret Hovell contributed to this report.