The pair faced an estimated 10,000 supporters in Wisconsin as Ryan returned Sunday to his home state for the first time in his new role.
"Hi mom," Ryan said, voice crackling, as he took the stage and looked out over a sprawling crowd.
An enthusiastic Romney seemed to feed off the energy.
"If you follow the campaign of Barack Obama, he's going to do everything in his power to make this the lowest, meanest, negative campaign in history. We're not going to let that happen. This is going to be a campaign about ideas, about the future of America," Romney said. "Mr. President, take your campaign out of the gutter. Let's talk about the real issues that America faces."
But Romney was reluctant to discuss in detail the plans Ryan crafted as chairman of the House Budget Committee.
The 42-year-old congressman proposed reshaping Medicare, the long-standing entitlement, by setting up a voucher-like system to let future retirees shop for private health coverage or choose the traditional program — a plan that independent budget analysts say would probably mean higher out-of-pocket costs for seniors.
Romney and Ryan, in their first joint television interview Sunday, were clearly mindful that some of Ryan's proposals don't sit well with key constituencies, among them seniors in critical states like Florida and Ohio.
Romney did not bring Ryan with him to the Sunshine State. The congressman's first stop there is expected next weekend, according to the campaign. Instead, Romney devoted Ryan's first solo swing to Iowa, a swing state Obama won convincingly four years ago.
Polls suggest the race will be closer this time.
While Ryan was expected to visit the Iowa State Fair in Des Moines, Obama's bus tour will begin in Council Bluffs, just across the Missouri River from Omaha, Neb., and heading across the state before wrapping up in Davenport along the Mississippi River.
Read more on Newsmax.com: In New Role, Ryan Faces Obama in Iowa