With four days left in the U.S. presidential campaign, Republican John McCain is mounting a furious last minute bid to overtake Democrat Barack Obama in the polls. The final days of the 2008 race for president.

Senator McCain focused on Ohio Friday. No Republican has ever won the presidency without winning Ohio, and the state has voted with the winning presidential candidate in the last 11 presidential elections.

"There's just four days left," he said. "The pundits have written us off, just like they have done before. But we are closing, my friends, and we are going to win in Ohio!"

McCain continues to pound Democrat Barack Obama on the issue of taxes and continues to question Obama's readiness to be commander in chief.

McCain's vice presidential running mate, Alaska Governor Sarah Palin, defended the Republican attacks on Obama at a rally in Pennsylvania.

"There is nothing mean-spirited or negative at all about calling someone out on their record, their plans and their associations," she said.

For his part, Senator Obama urged his supporters not to let up in the final days of the campaign, even though Obama leads McCain by an average of six points in national public opinion polls.

Obama campaigned Friday in the Midwest state of Iowa. Obama's victory in the Iowa party caucuses in January set him on a course to win the Democratic Party's presidential nomination.

"And what you started here in Iowa has swept the nation! We are seeing the same turnout, we are seeing the same people going and getting in line, volunteers and people participating," he said. "A whole new way of doing democracy started right here in Iowa, and it's all across the country now!"

In the final days of the campaign, high profile politicians from both parties are out trying to help the two candidates.

McCain is getting help from California Governor Arnold Scharzenegger and former New York City mayor Rudy Giuliani.

Obama has enlisted former President Bill Clinton and former vice president Al Gore.

Gore told a Florida rally Friday that an Obama victory would improve the U.S. image around the world.

"This is our chance, all of us, to say don't ever count America out," he said. "The United States of America is the miracle of world history. We are coming back! We are coming back!"

Gore urged Florida Democrats to vote early in advance of Tuesday's election. Gore's narrow loss in Florida eight years go to then Texas Governor George Bush cost him the presidential election.

McCain supporters are taking some last-minute encouragement from recent polls that suggest the race is tightening in key states like Indiana, Missouri, North Carolina and Pennsylvania.

But the Obama campaign is broadening its television advertising campaign in the final days to include the states of North Dakota and Georgia, states that have reliably supported Republican presidential candidates in recent years.

The Obama campaign will also begin airing ads in McCain's home state of Arizona in the wake of recent polls that show an unexpectedly close race there.

Both candidates will maintain an exhausting travel schedule through Monday as they look to lock up votes in the state-by-state electoral tally that determines who wins the presidency. The winning candidate must secure a minimum of 270 electoral votes out of a total of 538.