Clinton, speaking on "GMA," noted McCain's efforts to tone down the anger among his supporters.
"I think they've been negative, but I think Sen. McCain himself has publicly said that's not the direction he wants to go, and I appreciate that," she said.
McCain has made appeals to his audiences in recent days that they confront Obama's candidacy with respect, arguing that Obama is a "decent family man."
For McCain to win next month, he will have to do what no other presidential candidate has ever done -- come back from a 10-point deficit with only three weeks to go.
"No candidate has ever lost with a lead like this since modern polling began in 1936," ABC News' senior Washington correspondent George Stephanopoulos told "GMA."
Stephanopoulos said Obama's candidacy is riding a surge of public opinion, fueled by the current economic crisis, which is devastating for the Republicans.
A record number 90 percent of Americans feel the country is on the wrong track and 73 percent disapprove of President Bush's performance, according to the ABC/Post poll.
That disapproval number is also a record, and because Bush is a Republican, it makes it harder for McCain, the GOP candidate, to argue that he would be best to handle the economy.
Obama has also fared better in the debates.
More Americans, 32 percent, felt better about Obama after the first two debates. Only 12 percent had a better opinion of McCain after the first two debates.
The third and final showdown will be held Wednesday.
"It's McCain's last chance," Stephanopoulos said.
"McCain may be tempted in the last debate to go hard on the attack, but that could end up hurting him more than helping him in this environment," Stephanopoulos said.
McCain has surprised his critics before. He was counted out in the Republican primaries, only to come back and win the party's nomination.
"This is a tough campaign," McCain told ABC News' Charlie Gibson in an exclusive interview last week. "I'm the underdog. I've always been the underdog from the beginning."
ABC News' Kate Snow contributed to this report.