One Republican strategist estimated that hidden bias would add as many as three or four percentage points to McCain's current standing in the polls, which might give him a chance to win if he can make gains before Tuesday.
A record African-American vote for a presidential candidate, however, will likely work in Obama's favor. In key states, from Ohio to North Carolina, that could add at least a percentage point or more to the Democrat's margin.
Plouffe, the Obama manager, would not disclose turnout projections but said it exceeds the estimate of 130 million to 135 million votes by McCain pollster Bill McInturff.
That would top the record of 122 million cast in 2004 and might push turnout to levels not seen since the 1960s.
Last-minute campaigning reflects the calculations of both sides that the election will be won or lost largely in states that Bush carried in the closely contested 2004 election. McCain also targeted two states that John Kerry won - Pennsylvania and New Hampshire - in search of electoral votes he may fail to recover in Bush states such as New Mexico, Iowa and Colorado.
"The pundits have written us off again, as they have done before," he told supporters yesterday in Perkasie, Pa. "I know we're gonna win."
McCain plans a final, 24-hour sprint, dubbed the "Judgment Day" tour by aides, that will bring him to Phoenix on Tuesday. His final seven-state swing will also includes stops in Florida and Indiana, which went Democratic only once in the last 70 years, in 1964. It is now rated as a tossup after an intensive investment by Obama.
Privately, some Republican strategists have faulted the conduct of McCain's campaign and said his choice of Sarah Palin as his ticket mate made matters worse.
Polls suggest that she has turned off independent voters, a crucial swing group, even as she electrified her party's social and religious conservatives.
Davis, the McCain manager, said enthusiastic crowds continue to greet Palin, which shows that talk "about what a drag Governor Palin is on our ticket can't be further from the truth."
McCain has turned a gaffe by Obama's running mate, Joe Biden, into a campaign attack. The Delaware senator warned of an international crisis "to test the mettle" of Obama in his first six months as president, feeding voter concerns about Obama's inexperience and forcing the Democrats to run TV ads in battleground states in an attempt to contain any damage.
