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Paul Ryan will take on President Obama in the Iowa battleground Monday, splitting off on the campaign trail from Mitt Romney for his first solo swing as the newly minted Republican running mate.

The Wisconsin congressman is heading to the Hawkeye State as the focus of the race becomes -- for the time being -- all about him. On the heels of Romney's hastily called VP announcement Saturday morning, Ryan drew big crowds during a two-state bus tour Sunday and capped the day with an emotional homecoming at a Wisconsin rally.

Democrats, though, have wasted no time ramping up their attacks against him as they try to make hay out of the controversial Medicare plan he authored as House Budget Committee chairman. The Obama campaign went up with a new web video Monday morning timed for Romney's arrival in senior-heavy Florida. The ad ended with the message that is already a Democratic talking point: "Romney-Ryan, ending Medicare as we know it."

Obama will speak at two Iowa campaign stops Monday, in Council Bluffs and Boone. Ryan will hold a rally in Des Moines Monday afternoon.

Obama, at a fundraiser Sunday, offered his first comments on the GOP running mate pick. He welcomed him to the race, but called him the "ideological leader of the Republicans in Congress."

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"He is an articulate spokesman for Gov. Romney's vision. But it's a vision I fundamentally disagree with," Obama said.

Obama adviser David Axelrod, on "CBS This Morning," also likened the "excitement" surrounding Ryan to that surrounding the Sarah Palin pick in 2008. Axelrod said he thinks the selection of Ryan, who is popular with Tea Party figures, is "not going to be a plus for Mr. Romney."

Palin, though, vowed to help protect Ryan from the kinds of attacks she endured in 2008. On Fox News, she pledged to help make sure his reputation "won't be thrashed."

"We will call out the media for their lies and distortions as they try to thrash his reputation and his record," she said.

Romney and Ryan, on the bus tour Sunday, 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. Ryan says the plan is key to preserving Medicare by making it solvent.

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.

Romney, meanwhile, will be more than 1,000 miles away. The Republican presidential candidate has Florida events scheduled for St. Augustine and Miami.

Obama will showcase the powers of incumbency as he tours a farm in Missouri Valley, Iowa, and discusses ways of addressing a devastating drought afflicting a wide swath of the country. White House officials said the president planned to direct his Agriculture Department to buy up to $170 million worth of meat and poultry to provide relief to farmers and ranchers.

The president's bus tour was reminiscent of his Iowa caucus campaign four years ago, when he spent weeks mining for votes across the state. First lady Michelle Obama was expected to join the president for events in Dubuque and Davenport on Wednesday.

The Associated Press contributed to this report.