Romney, seeking to pull his campaign out of a summer slump, appeared to relish in campaigning alongside the youthful and energetic Ryan.
"This is Day Two for me," a gleeful Romney told a campaign rally in Moorseville, 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 competitive battleground state in the November election — as part of a multistate bus tour. The pair ended the day in Waukesha, Wis., with a homecoming-themed event for Ryan, who was in tears as he took the stage.
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 Obama's campaign. "Mr. President, take your campaign out of the gutter," he said.
Romney then planned to head to Florida and Ohio as the week begins, while Ryan was scheduled to travel to Iowa on Monday as the ticket looked to cover as much ground as possible.
For 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, an up and comer in Washington but far from a household name. Nearly 40 percent had never heard of him and 16 percent weren't sure what they thought of him.
The 42-year-old congressman embraced the attack dog role traditionally assumed by the No. 2 on the ticket. He said Obama had turned his 2008 campaign slogan of "hope and change" into "attack and blame."
"We're not going to fall for it," Ryan told a crowd of 5,000 in High Point, N.C.
Obama's campaign had already been trying to tie Romney to 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 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 Ryan's proposed budget cuts.
As chairman of the House Budget Committee, Ryan is the primary author of conservative tax and spending proposals that the tea party-infused Republican majority approved over vigorous Democratic opposition in 2011 and again in 2012.
They envision transforming Medicare into a program in which future seniors would receive government checks that they could use to purchase health insurance. Under the current program, the government directly pays doctors, hospitals and other health care providers.
Ryan and other supporters say the change is needed to prevent the program from financial calamity. Critics argue it would impose ever-increasing costs on seniors.
Other elements of the budget plan would cut projected spending for Medicaid, which provides health care for the poor, as well as food stamps, student loans and other social programs that Obama and Democrats have pledged to defend.
In all, it projects spending cuts of $5.3 trillion over a decade and would cut future projected deficits substantially. Romney, too, has proposed ambitious cuts in federal spending, but without the specifics that make Ryan's plan so attractive to fiscal conservatives and such a target for Democrats.
Republicans say Ryan could help put Wisconsin, which traditionally has voted Democratic in presidential campaigns, in play and that the Catholic Midwesterner also could appeal to blue-collar voters whom Romney, a Mormon and multimillionaire, has struggled to reach in Iowa and elsewhere.
Obama's campaign had no plans to start running new television ads in Wisconsin following Ryan's pick. Officials said they didn't think Ryan was popular enough statewide to swing Wisconsin toward the Republican ticket.