Hard-Fought Battle in Hard-Hit Ohio

(CNN) -- With a week to go before Election Day, most recent national polls show Democratic presidential nominee Barack Obama with an advantage. But how much are they to be believed?

The most recent national CNN poll of polls showed Obama with an 8-point lead over Republican presidential nominee John McCain, 51 percent to 43 percent. The polls were conducted October 21 through October 26.

Most other national polls show Obama with a lead ranging between 5 points and double digits.

A look at CNN polling during the same period before Election Day in 2000 and 2004 suggests that political observers and campaign supporters ought to be cautious in declaring the race over because of current polling numbers. See the latest state and national polls

When a presidential race has a non-incumbent in the lead, like this year, the poll numbers tend to tighten as Election Day gets closer, CNN senior researcher Alan Silverleib said.

"Any time it looks like they are on the verge of voting somebody new into office, there is buyer's remorse," he said. "Based on that, and the fact that the country has been so polarized in recent elections, there's pretty good reason to think that the polls might tighten up a little bit."

Four years ago, a national CNN poll of polls released about a week before Election Day showed President Bush leading Massachusetts Sen. John Kerry by 3 points, 49 percent to 46 percent.

The poll was released October 25 and reflected likely voters' choice for president. Election Day was November 2 in 2004.

A national CNN poll of polls released November 1 showed Bush leading Kerry by 2 points, 48 percent to 46 percent.

President Bush won by 3 percentage points, 51 percent to 48 percent.

In 2000, it was a bit of a different story. Election Day arrived November 7 that year.

A CNN/USA Today/Gallup tracking poll conducted October 29 through October 31 showed Bush, then the Texas governor, leading Democratic Sen. Al Gore, 48 percent to 43 percent. The poll had a margin of error of plus or minus 2 percentage points.

A subsequent poll conducted November 2 through November 4, released two days before the voters cast their ballots, showed the same results.

Gore, however, ended up winning the popular vote by about 540,000 votes. When broken down by percentage, both candidates had about 48 percent of the popular vote. Bush won the Electoral College, and thereby the presidency, by 5 electoral votes.

There have been a few examples of such "buyer's remorse" in recent history, Silverleib said.

"We saw that with [Arkansas Gov. Bill] Clinton in 1992, when the polls suddenly tightened up during the last week," he said. "It was almost like people saying, 'Do we really want this guy?' "

They did. Clinton soundly defeated President George H. W. Bush, 43 percent to 37 percent.

In another example, polls tightened during the 1968 presidential race between Republican Richard Nixon and Democrat Hubert Humphrey. Nixon led by double digits among registered voters in late September, according to a Gallup analysis published Monday.

The lead dwindled to 8 points in a poll conducted October 17 through October 22. By early November, Nixon was clinging to a 1-point lead. The poll was conducted October 29 through November 1 and surveyed likely voters, according to Gallup.

Nixon won by less than 1 percentage point.

"Humphrey had all the momentum at the end, and there's an open question there that had that election gone on for another week, Humphrey might very well had won," Silverleib said.

There is then the oft-cited example of Thomas Dewey and Harry Truman in 1948. Polls predicted that Dewey would win, but Truman pulled off the upset.

Silverleib, however, is reluctant to cite that race as illustrative of the accuracy of contemporary polls.

"People talk about Dewey and Truman, but they stopped polling a couple of weeks before the election," he said, adding, "polling then wasn't nearly as refined a science as it is now."

However, in what might be a bit of sobering news for the McCain campaign, since 1956, front-runners in late October lost the popular vote only twice after being ahead in the Gallup poll a week before Election Day, according to that polling organization's analysis.

Obama held a lead in both of Gallup's likely voter tracking polls released Tuesday.

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Sen. John McCain said Sunday he's "very happy" with the way his campaign is going, despite his "underdog" status in the polls.

"We're going to be in a tight race and we're going to be up late on election night. That's just -- I'm confident of that. I've been in too many campaigns, my friend, not to sense that things are headed our way," McCain said Sunday on Fox News.

Sen. Barack Obama leads McCain by 6 points, according to CNN's latest average of national polls.

"I love being the underdog. You know, every time that I've gotten ahead, somehow I've messed it up," the Republican candidate said.

Asked if Gov. Sarah Palin has become a drag on his ticket, McCain said, "As a cold political calculation, I could not be more pleased."

"She has excited and energized our base. She is a direct counterpoint to the liberal feminist agenda for America. She has a wonderful family. She's a reformer. She's a conservative. She's the best thing that could have happened to my campaign and to America," he said.

In response to a question from Fox's Chris Wallace, McCain said he has considered the possibility that he could lose, but added, "I don't dwell on it."

"I've had a wonderful life. I have to go back and live in Arizona, and be in the United States Senate representing them, and with a wonderful family, and daughters and sons that I'm so proud of, and a life that's been blessed," he said.

"I'm the luckiest guy you have ever interviewed and will ever interview. I'm the most fortunate man on earth, and I thank God for it every single day."

McCain said if things don't turn out his way on Election Day, "Don't feel sorry for John McCain, and John McCain will be concentrating on not feeling sorry for himself."

CNN's latest poll of polls shows Obama drawing 49 percent of voters nationwide, while McCain stands at 43 percent.

The 6-point lead represents no change from a CNN poll of polls released late last week, though it is 2 points smaller than one week ago.

The national poll of polls consists of three surveys: Reuters/C-SPAN/Zogby (October 15-17), Gallup (October 15-17) and Diageo/Hotline (October 15-17). It does not have a sampling error.

McCain on Sunday was campaigning in Ohio, the state that put President Bush over the top in his re-election bid four years ago.

The Arizona senator had rallies scheduled in Westerville and Toledo, Ohio.

The most recent CNN poll of polls in Ohio suggests that 48 percent of voters there are backing Obama and 46 percent are supporting McCain.

Obama on Sunday was campaigning in North Carolina, a once reliably Republican state in presidential contests that is now up for grabs.

The last Democratic presidential candidate to win North Carolina was Jimmy Carter in 1976. The most recent CNN/Time Magazine/Opinion Research Corporation poll in the state has the contest deadlocked at 49 percent for each candidate.

Obama's campaign events come on the heels of a big endorsement from Colin Powell, the former secretary of state. Watch what Powell says about Obama »

"I think he is a transformational figure, he is a new generation coming onto the world stage, onto the American stage, and for that reason I'll be voting for Sen. Barack Obama," Powell said as he announced his endorsement Sunday on NBC's "Meet the Press."

As for the running mates, Palin on Sunday had a rally scheduled in New Mexico, a state that narrowly went for President Bush four years ago.

Democratic vice-presidential nominee Joe Biden was holding a campaign rally in Tacoma, Washington, on Sunday. Recent polls in that state suggest Obama has a 10 point lead there.