But, says CBS News Senior White House Correspondent Bill Plante, a comeback isn't entirely out of the question.
Most polls have McCain down anywhere from 3-to-13 points. Still, Plante points out, he's been counted out before and come from behind.
So, what are McCain's chances of pulling off any upset?
"It's rare at this stage ... that candidates will come from behind and win," says James Thurber, director of the Center for Congressional and Presidential Studies at American University.
But, Plante notes, it's happened before. In 1980, Ronald Reagan trailed Jimmy Carter in the polls, but surged ahead in the last week following their only debate.
"He turned the election into a referendum on Carter and what Carter had done the previous four years," Thurber explained.
In 1968, Hubert Humphrey almost overtook Richard Nixon "promising to get out of the war in Vietnam and that got a lot of people excited about him and he almost won," Thurber says.
Al Gore was down by 12 points in 2000, and came back to win the popular vote, though not the election.
So, what would it take in 2008?
"What it would take," Thurber says, "is to have a clear strategy theme and message by McCain on the economy and have people believe in it."
This year, early voting means the choices of millions of voters are already locked in.
"If some event occurs in the next (seven) days to help McCain," Thurber observed, "he may still lose, because a whole lot of people have already voted for Obama."
Another problem, Plante says" There simply aren't that many undecided voters left -- perhaps five percent.
So, the bottom line, according to Plante: A McCain comeback is possible, but it would take a very large swing of already committed voters.