The crowd in Madison was estimated at more than 10,000, one of the biggest Romney has had.
Bringing aboard the seven-term Wisconsin congressman, a rock star to the tea party, gave a jolt of energy to the campaign, after weeks in which Romney struggled to escape Democrats' efforts to paint him as a heartless former private-equity executive who cannot relate to the middle-class citizens who they say would be hurt by his policies.
"Mr. President, take your campaign out of the gutter," Romney thundered, not long after he chastised a protester to show some respect and listen to others. "Talk about the real issues America is facing."
But lurking beneath the surface was the heat, and potential risk, generated by Ryan's proposal to cut the budget - and to convert Medicare from a guaranteed federal health benefit to a system of grants for future seniors to buy private insurance.
Romney is taking a gamble that the public is ready for a substantive discussion about the hard steps Ryan says are needed to avert a fiscal calamity.
Romney said his own budget plan, not the more detailed proposals of his partner, would be the basis of his White House bid.
"I have my budget plan," he said. "And that's the budget plan we're going to run on."
He also addressed the matter in a 60 Minutes interview that aired Sunday night.
Romney and Ryan, in their first joint TV interview, sought to reassure older voters that they wouldn't take away their benefits, with Ryan saying his mother is "a Medicare senior in Florida" and Romney vowing there would be "no changes" for seniors currently counting on the popular federal program.
Ryan said he planned to release two years of personal tax returns to the public. 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.
President Obama, campaigning in Chicago, said the GOP ticket was pushing "trickle-down fairy dust," slashing spending that helps the middle class and the poor while cutting taxes more deeply for wealthier taxpayers.
In the warm-up to the homecoming rally, Rep. James Sensenbrenner (R., Wis.) acknowledged a Romney administration "will be controversial and will cause pain" as he urged the crowd to resist the "lies" Obama and his Democratic allies will spread.
After the event, Romney left to campaign in Florida, with its large population of elderly Medicare beneficiaries, while Ryan split off for Des Moines, Iowa.
Obama has been leading consistently in Florida polls, but Romney has enjoyed a consistent advantage with older voters there.
"It's too simplistic to assume that older voters are now going to run away from Romney," said Peter A. Brown, assistant director of the Quinnipiac University poll who is a Florida resident. "What is clearly true is that older voters are concerned about the debt and the economy."
The challenge for the Romney campaign, he said, will be to reassure older voters that any changes to Medicare will not affect them and to convince them that it's important to solve the problem of entitlement costs and the national debt so their children and grandchildren are not saddled with it.
"Social Security and Medicare have always been volatile issues, but the country is in a different situation now," Brown said. "There is more appreciation for the long-term fiscal problems of the nation."
Obama has led steadily in Wisconsin polls, but the giddy reaction to the Ryan pick caused some Republicans to wonder aloud if he might help clinch the state for the GOP.
In 2010, Ryan won reelection in his southeastern Wisconsin swing district with 68 percent of the vote, and with 64 percent in 2008. By contrast, the GOP presidential nominee in 2008, John McCain, received 47 percent in the district.
"I like Ryan - he's not a typical politician," said Donald Erickson, 68, a retired electrical engineer from a Milwaukee suburb who drives a shuttle van. "He is not going to tell you what he thinks you want to here. He has serious ideas."
He said it was clear that Ryan's plan would leave current Medicare recipients alone, and he said he was more angry at cuts in doctors' payments under the Obama administration's health-care overhaul.
"I'm definitely going to vote against Obama," he said.
Contact Thomas Fitzgerald
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This article contains information from the Associated Press.