Left: US President Barack Obama waves as he walks to a campaign fundraising event in his neighborhood in Chicago, August 12, 2012. Right: Republican US presidential candidate Mitt Romney (R) shakes hands with vice president running mate US Congressman Paul Ryan (R-WI) during a campaign event in Waukesha, Wisconsin August 12, 2012. [Photos/Agencies]

DES MOINES, IOWA - Newly tapped Republican vice presidential contender Paul Ryan is facing off against President Barack Obama as the front lines in the battle for the White House shift to Iowa.

While Mitt Romney continues a Florida bus tour, Ryan will meet voters at the Iowa State Fair, campaigning alone for the first time in the same state where Obama launches a bus tour of his own. Monday's events may help determine whether conservative excitement for the Wisconsin congressman — and his controversial budget plans — will overshadow Romney's own economic message.

Democrats are banking on it.

Since Romney formally named Ryan his running mate on Saturday, the Obama campaign has been attacking the Republican budget architect's plans to transform Medicare into a voucher system and re-shape the nation's tax system. That effort will continue as Obama kicks off a three-day bus tour across Iowa, making his longest visit to a single state yet as he seeks to fire up supporters who put him on the path to the presidency in 2008.

Ryan figures to play prominently in Obama's message.

Attending campaign fundraisers in Chicago, the president tagged 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," Obama said Sunday in his first public comments about Ryan's selection.

Romney tried to distance himself from his running mate's budget plan, making clear that his ideas rule, not Ryan's.

"I have my budget plan," Romney said, "And that's the budget plan we're going to run on."

He walked a careful line as he campaigned with Ryan, a tea party favorite, by his side in North Carolina and Wisconsin, singling out his running mate's work "to make sure we can save Medicare." But the presidential candidate never said whether he embraced Ryan's austere plan himself.

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.

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 discuss 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 Defense Department, a large purchaser of beef, pork and lamb, was expected to look for ways to encourage its vendors to speed up purchases of meat.

Obama has urged Congress to pass a farm bill to provide a long-term solution for farmers, a point he was expected to make in Iowa, whose economy is heavily dependent on agriculture.

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.