BELMONT, Massachusetts — US President Barack Obama and rival Mitt Romney prepared for Wednesday's debate this weekend, leaving their running mates to spar over policy and seek votes in key swing states.

With the president off the campaign trail just 38 days before Americans vote on November 6, Romney spent a quiet day in Massachusetts, visiting the home of son Tagg in a Boston suburb and, according to his campaign, steering clear of debate preparation.

But with both men seeking an edge in their crucial first face-off of the campaign, they will undoubtedly be spending the bulk of their time between now and Wednesday's debate in preparation for the showdown in Denver, Colorado, one of about a dozen swing states where voters will determine the election.

Obama travels to Nevada for an event on Sunday, and spends the next two days in the town of Henderson gearing up for Wednesday, according to the White House.

Both sides began their debate spin weeks ago, seeking to set high expectations for their opponent, which they could then declare he failed to meet, while setting the bar low for their own candidate.

Democrats say Romney is a challenging debater who honed his skills with about 20 debates in the Republican primaries. Republicans counter that Obama is seasoned with several presidential debates against John McCain in 2008.

Romney, who trails Obama in the polls, suggested he would do well at the debates, provided Americans do not merely seize on the "theatrics" of one-liners but focus on real issues.

"The American people will listen carefully to the conversation... and they'll decide who can help their family, who will be able to get our economy going in the way it could be going and they'll make their decision based on what they believe is in the best interest of the country and their own family," Romney told reporters Friday.

"And I expect to be able to describe that in a way people will understand, and if they do, I'll get elected."

With Obama and Romney hunkered down, the campaign trail was wide open for Vice President Joe Biden and Romney's running mate Paul Ryan.

Stumping Saturday in Florida, a large battleground state with millions of senior voters, Biden hit out at the Republicans' plans to overhaul Medicare, the government health care program for nearly 50 million retirees and disabled Americans.

"This country is facing... the starkest choice for president that we've faced, at least in my memory," Biden told a crowd in Fort Myers.

"The truth of the matter is that nowhere is it more clear what they would do than in Medicare."

Romney and Ryan seek to inject greater competition by converting Medicare's guaranteed benefits into vouchers that can be used to purchase private insurance or traditional Medicare coverage.

Republicans say it saves money, but Democrats argue it would expose millions of elderly to rising health care costs.

And with polls showing most seniors in the key swing states Florida, Ohio and Virginia opposing Republican plans to overhaul Medicare, Biden twisted the knife on his rival.

"What governor 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, referring to Ryan's plans to overhaul Medicare.

"He picked Paul Ryan because Paul Ryan does represent the ideological -- how can I say it? -- the center of the Republican Party in the House of Representatives."

Hitting the hustings in Derry, New Hampshire, Ryan decried what he said was Obama's ever-present threat to grow government and saddle the country with more debt.

"We need to tackle our nation's challenges before they tackle us," he said.

"We need to save and strengthen Medicare and Social Security, and we're putting the ideas on the table on how to do that."

Hours later in the key swing state of Ohio, where polls show Obama up by an average of five percentage points, Ryan took it a step further.

"Let me be very clear: there is only one person in this race threatening the health and retirement security programs of our seniors, and that is President Obama," he said.

"Shame on the politician who wants to use this issue to try and scare seniors, when those of us are trying to fix this problem for my generation and my kids' generation and your kids."

Ryan embarks Monday on a two-day bus tour across Iowa before he heads to Virginia Wednesday for three solid days of debate camp, his campaign said.

While the presidential contenders have three debates, Biden and Ryan have just one shot against each other, on October 11 in Kentucky.