Democrat Barack Obama is extending his campaign advertising into traditionally Republican territory, as polls there show him closing on rival John McCain.
Mr Obama is to run ads in Arizona, his rival's home state, as well as Georgia and North Dakota, with only three days to go before the presidential election.
On Friday Mr Obama's campaign took him from the state of Iowa to Indiana.
Meanwhile, California Governor Arnold Schwarzenegger gave Mr McCain strong backing in the swing state of Ohio.
In a rousing speech, the former Hollywood film star said the Republican candidate was the real action hero.
Arnold Schwarzenegger attacks Obama's spending
"John McCain has served this country longer in a [prisoner of war] camp than his opponent has served in the United States Senate," said the star of The Terminator, Predator and Conan the Barbarian.
Speaking to big crowds at a rally in Iowa and Indiana, Mr Obama warned Mr McCain's campaign was likely to escalate into a final crescendo of attacks on him.
Voters would see "more of the slash-and-burn, say-anything, do-anything politics that's calculated to divide and distract, to tear us apart, rather than bring us together", he said in Des Moines, Iowa.
The Illinois senator then made a brief stop in his home city of Chicago to see his two young daughters at Halloween before moving on to Indiana, where he addressed more than 40,000 supporters in Highland, Indiana.
Meanwhile, former Vice-President Al Gore campaigned for Mr Obama in Florida, another important swing state.
He referred to his own defeat there in 2000, saying "it's been a long eight years" - and urged Florida's voters to "make good" on the challenge of electing Mr Obama as president.
The Obama campaign plans to run two adverts in North Dakota and Georgia, both states which have usually voted Republican.
One seeks to link Mr McCain, 72, to President George W Bush, suggesting the Republican would continue the same economic policies.
The other relies on Mr Obama's message of "unity over division", highlighting his endorsement by such high-profile Republican figures as former Secretary of State Colin Powell.
If the polls hold, the American people will elect Barack Obama as their 44th president... And he would be a very bad choice
Peter Wehner Former deputy assistant to President Bush
Polls suggest Mr Obama is closing the gap on Mr McCain in Georgia, with a CNN/Time/Opinion Research poll giving the Republican a five-point lead among likely voters.
The same poll shows third-party candidate Bob Barr, a Libertarian and former Georgia congressman, with 4% support, which could affect the race.
By early Friday, some 31% of voters in Georgia had chosen to take advantage of early voting and cast their ballot in advance. Obama aides said the numbers were "highly encouraging".
McCain campaign manager Rick Davis dismissed the advance into Republican territory, saying he advised Mr Obama, 47, to focus his spending on states which Mr McCain intended to prise from him on 4 November.
Mr Davis also told reporters that the campaign was "jazzed up" about Mr McCain's prospects, saying that he was living up to his reputation as the underdog who fights back.
"We are witnessing, I believe, probably one of the greatest comebacks that you've seen since John McCain won the primary," he said.
Mr McCain told a crowd of several thousand in Steubenville, Ohio, that he felt his campaign had a new momentum in the state.
"You're going to be the battleground state again," he said. "You're going to be the one who decides. I need Ohio and I need you."
Earlier, he told a rally in Hanoverton that Mr Obama was "in the liberal left-lane of politics" and intended to raise their taxes.
Ex-New York Mayor Rudy Giuliani, campaigning for his former rival for the Republican nomination, said Mr McCain was the candidate sticking up for ordinary Americans.
"He's going to fight to see that your taxes are low and that the economy recovers," he said.
Mr McCain's running mate, Sarah Palin, in Pennsylvania also focused on the economy, telling supporters that Mr Obama was "for bigger government and he's going to raise your taxes".
The McCain campaign's efforts come a day after the Arizona senator made a late plea for donations in an effort to pull off a surprise victory.
His appeal to supporters came less than a day after Mr Obama spent an estimated $5m (£3.1m) on a 30-minute primetime "infomercial" aired on US TV networks.
Mr McCain is spending two days campaigning in Ohio, which is seen as a must-win state if he is to have any chance of overall victory.
The latest national poll by CBS and the New York Times puts him 13% behind the Illinois senator.
Polls in battleground states suggest the differences in support between the two candidates are much slimmer.