PUEBLO, Colo. — Barack Obama and John McCain sprinted through a dwindling number of battleground states today, appealing for votes by returning to the core arguments of their candidacies with time running out.

Obama seized on a rare campaign appearance by Vice President Dick Cheney to drive home his theme that electing McCain would represent a continuation of the failed policies of the Bush administration. Speaking in Laramie, Wyo., Cheney declared that McCain is "the right leader for this moment in history," and Obama responded to the endorsement at a rally here in Pueblo.

"I'd like to congratulate Senator McCain on this endorsement because he really earned it," Obama said. "He served as Washington's biggest cheerleader for going to war in Iraq and supports economic policies that are no different from the last eight years."

Campaigning in Springfield, Va., McCain reiterated his contention that Obama is too liberal and inexperienced for the presidency and continued to cast doubt on the Democratic nominee's patriotism. McCain pointed to Obama's remark in Des Moines on Friday that his victory in the Iowa caucuses in January had "vindicated" his faith in America.

"My country has never had anything to prove to me, my friends," McCain told the crowd as it loudly booed Obama. "I have always had faith in it, and I have been humbled and honored to serve it."

Meanwhile, spokesmen for the two campaigns continued their own counterattacks. McCain spokesman Tucker Bounds shot back at Obama's comments about Cheney by pointing out that Obama and the vice president were distantly related and "shared support for the Bush energy policy and the out-of-control spending that John McCain has fought to oppose." Obama spokesman Bill Burton repeatedly defended the Democratic nominee on the Iowa comment, accusing McCain of twisting Obama's words.

Both Virginia and Colorado voted for President Bush in 2004 but are now considered to be leaning toward Obama. Early voting ended in Colorado on Friday, and turnout was heavy, but Obama urged supporters to scour their neighborhoods and workplaces for holdouts and help get them to the polls on Tuesday. "We have a righteous wind at our backs," he said.

Obama ended the day in Springfield, Mo., in the state's conservative southwest corner. The rich pocket of votes is home to Missouri State University and is the sort of redoubt typically ignored in the final days of a presidential campaign. But Obama campaign officials view Missouri as a battleground state still up for grabs, along with North Carolina, Indiana and Georgia. The Obama campaign believes it is ahead in the other big prizes of Pennsylvania, Ohio and Florida.

Nor does the picture appear to be changing nationally. The Washington Post-ABC News tracking poll released yesterday showed Obama holding a 53 percent to 44 percent national lead over McCain, unchanged from Friday, and with few hopeful signs for the GOP nominee.

For the first time in the poll, the slice of likely voters who report they will "definitely" vote for Obama has reached 50 percent, a milestone that George W. Bush never reached in Post-ABC tracking polls from 2000 or 2004. And the number of voters who said they could still change their minds has declined to 7 percent.

The poll found McCain gaining little traction with his arguments that Obama represents a risky choice and that he himself is the better candidate on such issues as taxes and the economy. For the second time in Post-ABC polling, Obama has crossed into majority support as the candidate better able to manage an unexpected crisis.

Today, Obama will head to Ohio for events in Columbus, Cleveland and Cincinnati. He is scheduled to spend tomorrow in Florida, North Carolina and Virginia, where he will hold a rally in Manassas before flying home to Chicago. He will make a brief stop in Indiana on Election Day.

McCain was scheduled to appear on "Saturday Night Live" and then return to Pennsylvania today before heading to New Hampshire, the state that revived his presidential bid in January by delivering him a vital primary victory. He will then hold a midnight rally in Miami and plans to spend the final 24 hours before Election Day in six states: Florida, Virginia, Pennsylvania, Indiana, New Mexico and Nevada, before returning to his home in Prescott, Ariz.

The Obama campaign grew nervous last week when initial early-voting returns suggested that young voters were not showing up in strong numbers. But the volume picked up later in the week, and the campaign hastily added new rounds of text messages and scheduled additional get-out-the-vote concerts and other outreach events.

But at a rally yesterday morning in Henderson, Nev., Obama alluded to the mandate that a big victory would provide.

His chief strategist, David Axelrod, said later that the narrow electoral map of previous elections "impeded our ability to solve problems," adding, "To the extent that you can do better, it's helpful."

In Northern Virginia, McCain — as he has in recent speeches — devoted a significant portion of his remarks to Obama's brief exchange with Joe Wurzelbacher, the Ohio man immortalized by McCain as "Joe the Plumber," saying it showed the Democrat would tax wealthy Americans to pay for his spending priorities.

"Joe's dream is your dream, to own a small business that will create jobs," McCain said.

"He's a Marxist!" one member of the crowd cried, while another shouted, "Regular Americans for McCain!"