The first of three presidential debates is scheduled for Wednesday, Oct. 3 in Denver, Colo. (Dawn Megli/Neon Tommy)

Both candidates have begun preparations for the showdown looming four days from now in Denver, Colo., which will feature six time segments devoted to domestic policy. Obama will hold practice debates with Sen. John Kerry (D-Mass.), who will be playing Romney. Ohio Sen. Rob Portman will assume the role of Obama during Romney's mock debates, CBS News reported.

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With the subject of taxes expected to factor into the first debate, both candidates offered a preview of the verbal tussling that could lie ahead.

"My opponent thinks it's fair that somebody who makes $20 million a year like he does pays a lower tax rate than a cop or a teacher who makes $50,000," Obama told a crowd at a Friday campaign appearance.

Romney said during one stop, "I will not raise taxes on middle income Americans," saying that the president has been misrepresenting his record.

For Obama, Wednesday night is his opportunity to rejuvenate the voter enthusiasm that lifted him into the White House in 2008. Romney faces the daunting task of trying to erase a forgettable September marred by gaffes about the 47 percent and Middle East peace.

From the Associated Press:

Obama, no longer the fresh face of 2008, must convince skeptical Americans that he can accomplish in a second term what he couldn't in his first, restoring the economy to full health.

Romney, anxious to keep the race from slipping away, needs to instill confidence that he is a credible and trusted alternative to the president, with a better plan for strengthening the economy.

Both camps have tried to downplay expectations for their respective candidates, according to USA Today.

A Romney senior adviser said that Obama is a "universally-acclaimed public speaker" who has more experience in one-on-one presidential debates than the former Massachusetts governor. Meanwhile, Obama aides said Romney has sharped his debating skills through 20 debates during the GOP primary.

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While neither candidate had public events planned for Saturday, their running mates continued to crisscross the country for votes.

GOP vice presidential nominee Paul Ryan stumped in the toss-up state of New Hampshire, praising Romney's leadership in Massachusetts and blaming Obama for the nation's credit downgrade, CNN reported.

“You have a responsibility to talk to your fellow citizens, to get those people that liked the promise of hope and change four years ago but are demoralized now, to show them we have a better path, we have better ideas, because we are going to reapply our founding principles,” Ryan said.

Vice President Joe Biden's speech in Fort Myers, Fla., geared toward courting retirees and white, working-class voters, focused on the Medicare cuts proposed by Romney's running mate.

"What Gov. Romney did in picking Paul Ryan is he has given clear definition to all those vague assertions he was making during his primary campaign," Biden said. "[And] nowhere is it more clear what they would do than in Medicare."

The Denver debate airs live at 6 p.m. PDT on Oct. 3. The two candidates square off again on Oct. 16 and Oct. 22. Biden and Ryan will have their only debate on Oct. 11.

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