Both the candidates hit the campaign trail hard again on Wednesday, with Barack Obama holding a rally in Virginia and John McCain in Pennsylvania and New Hampshire.
McCain, warned Obama not to become used to his comfortable lead in the polls Wednesday as he attacked the Democrat's plans to "redistribute wealth".
The Arizona senator has attempted to cast Obama's tax plans as being part of a "socialist agenda".
"After all, before government can redistribute wealth, it has to confiscate wealth from those who earned it," he said.
"And whatever the right word is for that way of thinking, the redistribution of wealth is the last thing America needs right now."
McCain also repeated the line that "the next president won't have time to get used to the office" and insisted that the country needed a "fighter" who doesn't "invite testing".
'Out of ideas'
Republicans had seized on comments by Joe Biden, Obama's running-mate, earlier this week that enemies of the US would seek to test Obama at an early stage if he was elected on November 4.
Obama rejected the attacks on his experience and tax policy, dismissing his Republican foe as "out of ideas".
"Whoever is the next president is going to have to deal with a whole host of challenges internationally, and that a period of transition in a new administration is always one in which we have to be vigilant," Obama said in a campaign speech in Virginia.
"It's not a very plausible argument that he's making right now. And I think it's an indication that they have run out of ideas," said Obama.
"They have been trying to throw whatever they can up against the wall to see what sticks and this is their latest version."
Al Jazeera's James Bays in Virgina said the event, which included some of his senior foreign policy advisors, was designed to make Obama look more presidential.
The Illinois senator is set to leave the campaign trail on Thursday to visit his sick grandmother in Hawaii.