(CNN) -- The 2012 presidential campaign returned its focus to Iowa on Monday as President Barack Obama and Rep. Paul Ryan, the newly minted GOP vice presidential candidate, stumped in the electoral battleground.
Elsewhere, Mitt Romney continued his campaign bus tour at events in Florida and Vice President Joe Biden was slated to rally in North Carolina, making Monday the first day all four candidates vying for president and vice president hit the trail.
The focus for all four remained on Ryan, who was unveiled as Romney's running mate at a Saturday morning event in Virginia. A CNN/ORC poll taken at the beginning of August showed a majority of Americans were unfamiliar with Ryan, leaving an opening for both Democrats and Republicans to offer their own definitions of the seven-term Wisconsin congressman.
Ryan was met by a small group of hecklers when he tried to deliver a speech during his much-anticipated first solo stop since becoming Romney's running mate.
Speaking to a crowd from a soap box at the Iowa State Fair, Ryan was disrupted by activists, one relentlessly shouting, "Stop the war on the middle class." Two women tried to climb on the platform next to the congresswoman, and both were carried off by police and other officials.
Ryan acknowledged the protesters before continuing with his stump speech.
In St. Augustine, Romney called Ryan "a man who has proven that he knows how to solve problems," pointing to his budget plan that seeks to slash the federal debt and deficit.
Yet it's that very plan that Democrats, including Obama, seized upon in the hours after Romney announced he had selected Ryan as his running mate, latching specifically onto his proposals for Medicare, the government-run health care program for senior citizens.
Ryan's proposals, first introduced in 2011, include the provision that Medicare-approved private insurers would one day compete with traditional Medicare on an exchange. The proposal would affect Americans currently under age 55. The plan's opponents, who include most Democrats, say that would increase the financial burden on senior citizens.
Saying Ryan is "a good guy, a decent guy," Biden said his rival's House budget proposal "has given definition to the vague commitments that Romney's been making."
"They called it 'gutsy.' Gutsy. I'm serious. What's 'gutsy' about giving millionaires another tax break? What's gutsy about gutting Medicare, Medicaid, education?" Biden asked.
Rep. Debbie Wasserman Schultz of Florida, the chairwoman of the Democratic National Committee, also took a shot at the proposal Monday. "Mitt Romney and Paul Ryan both want to end Medicare as we know it. They both want to shred the safety net," she said on CNN's "Starting Point with Soledad O'Brien."
Ryan, the House budget committee chairman, said Sunday the intention of his plan is to remake Medicare so that it remains financially soluble for future generations.
"My mom is a Medicare senior in Florida," he said on CBS. "Our point is we need to preserve their benefits, because government made promises to them that they've organized their retirements around."
"In order to make sure we can do that, you must reform it for those of us who are younger," he continued. "And we think these reforms are good reforms that have bipartisan origins."
On Monday, Romney said he and Ryan "want to make sure we preserve and protect Medicare."
Romney's Monday rally -- his first solo appearance since his vice presidential announcement -- was closely watched by politicos and the media after he drew larger-than-usual and very enthusiastic audiences at events with Ryan over the weekend.
Monday morning, the Orlando Sentinel reported Romney canceled a third Florida event due to exhaustion from his busy weekend. Campaign spokesman Kevin Madden pushed back on that report, saying Romney had a "packed schedule and a full day" including meetings with staff.
Ryan was set to stump Monday at the Iowa State Fair, the site of last summer's surprise straw poll win for then-presidential candidate Rep. Michele Bachmann. The state, known for its first-in-the-nation presidential caucuses, is shaping up to be a battleground again in November. An NBC/Marist poll taken in May showed Romney and Obama tied at 44%.
Obama began a three-day blitz of Iowa on Monday. The state ignited his 2008 primary charge against Hillary Clinton and later handed him a 10-point victory over Sen. John McCain.
In remarks in Council Bluffs, Obama addressed the ongoing drought affecting nearly half of the continental United States, saying it is time for Congress to act on passing drought relief for farmers and ranchers whose livelihoods are on the line.
Obama specifically called out Ryan, saying he and others in Congress are stalling for political gain.
"I am told that Gov. Romney's new running mate Paul Ryan will be around Iowa in the next few days, and he is one of the congressmen standing in the way," Obama told the crowd. "So if you happen to see Congressman Ryan, tell him how important this farm bill is to Iowa and the rural communities, because we have to put politics aside when it comes to doing the right thing for rural America and for Iowa."
Brendan Buck, a spokesman for Ryan, responded that, "No one will work harder to defend farmers and ranchers than the Romney-Ryan ticket."
Obama's seven-city tour, lasting through Wednesday, will include stops in Council Bluffs, Boone, Oskaloosa, Marshalltown, Waterloo, Dubuque and Davenport.
Romney aides said this weekend that Romney and Ryan will campaign separately until the Republican convention this month in Tampa.
Romney aide Brendan Buck said Ryan would campaign in central Florida next weekend, a rebuff to critics who said the vice presidential candidate was skipping Romney's stops in Florida this week to avoid questions about his Medicare proposals from senior citizens there.
CNN's Ashley Killough, Rachel Streitfeld and Alexander Mooney, and CNNMoney's Lex Haris contributed to this report.