WAUKESHA, Wis. -- Cheered by the biggest crowds of his campaign, Republican Mitt Romney declared Sunday that 42-year-old running mate Paul Ryan is ready to be president, but said his own budget plan, not the more detailed proposals of his partner, will be the basis of his White House bid.
"I have my budget plan," Mr. Romney said. "And that's the budget plan we're going to run on."
Mr. Romney had walked a careful line earlier Sunday as he campaigned with Mr. Ryan in North Carolina, singling out his running mate's work "to make sure we can save Medicare."
But the presidential candidate never said whether he embraced Mr. Ryan's austere plan himself, and he addressed the matter more directly in a 60 Minutes interview that aired Sunday night on CBS.
Democrats weren't about to let them off that hook.
President Obama, attending campaign fund-raisers Sunday in Chicago, tagged Mr. Ryan as the "ideological leader" of the Republican Party.
"He is a decent man, he is a family man, he is an articulate spokesman for Governor Romney's vision, but it is a vision that I fundamentally disagree with," Mr. Obama said in his first public comments about Mr. Ryan's selection.
Obama adviser David Axelrod and other aides spent Sunday trying to brand Mr. Ryan's budget "the Ryan-Romney plan."
During the Republican primary, Mr. Romney had called Mr. Ryan's budget a "bold and exciting effort" that was "very much needed."
Mr. Ryan proposed to reshape Medicare by setting up a voucher-like system to let future retirees shop for private coverage or choose the traditional program -- a plan that independent budget analysts say probably would mean smaller increases in benefits than current law would provide.
Mr. Romney and Mr. Ryan, in their first joint television interview Sunday, clearly mindful that some of Mr. Ryan's proposals don't sit well with key constituencies, among them seniors in critical states such as Ohio and Florida.
Each man sought to reassure older voters they wouldn't take away their benefits, with Mr. Ryan saying his mother is "a Medicare senior in Florida" and Mr. Romney vowing there would be "no changes" for seniors currently counting on the popular federal program.
"In America, the nature of this country has been giving people more freedom, more choices," Mr. Romney said. "That's how we make Medicare work down the road."
Mr. Romney praised his running mate for his policy depth and analytical skills.
The presumptive presidential nominee said Mr. Ryan, "if it were necessary, could become president." And Mr. Romney extolled his running mate's Washington experience, despite having criticized primary rivals Newt Gingrich and Rick Santorum for their years in the nation's capital.
Mr. Ryan said he planned to release two years of personal tax returns to the public.
The wealthy Mr. Romney is also releasing two years of returns, despite pressure from Democrats and some Republicans to provide more information about how he manages his millions.
Campaigning over the weekend, Mr. Romney appeared to relish in campaigning alongside the energetic Mr. Ryan, 42.
"This is Day Two for me," a gleeful Mr. Romney told a campaign rally in Mooresville, N.C. "This is Day Two on our comeback tour to get America strong again, to rebuild the promise of America."
He meant a comeback for the country, but that could apply as well to his campaign.
The duo blitzed through North Carolina -- a battleground state in the November election -- as part of a multistate bus tour.
They ended the day in Waukesha, Wis., with a homecoming-themed event for Mr. Ryan, who was in tears as he took the stage.
Mr. Romney, emboldened by the enthusiastic crowds that greeted the pair Sunday, wrapped up a day of campaigning with a sharp shot at the tone of Mr. Obama's campaign.
"Mr. President, take your campaign out of the gutter," he said.
Mr. Romney then planned to head to Florida and Ohio as the week begins, while Mr. Ryan was scheduled to travel to Iowa today as the ticket looked to cover as much ground as possible.
For Mr. Ryan, the weekend of campaigning was a chance to make a first impression on many voters.
A recent CNN/ORC international poll found a majority of voters had no opinion of the congressman.
Nearly 40 percent had never heard of him and 16 percent weren't sure what they thought of him.
Mr. Ryan embraced the attack dog role traditionally assumed by the No. 2 candidate on the ticket.
He said Mr. Obama had turned his 2008 campaign slogan of "hope and change" into "attack and blame."
"We're not going to fall for it," Mr. Ryan told a crowd of 5,000 in High Point, N.C.
The Obama campaign had already been trying to tie Mr. Romney to Mr. Ryan's tough budget blueprint even before the Wisconsin congressman emerged as a contender for the GOP ticket.
Democrats believe seniors, those nearing retirement, and middle-income voters will view Mr. Ryan's long-term budget plan remaking Medicare and cutting trillions in federal spending as a threat to their financial security.
Campaign officials were readying state-specific strategies aimed at seniors in Florida and Ohio, and also planned to court young people and military service members who they believe will be turned off by other elements of Mr. Ryan's proposed budget cuts.