President Barack Obama's campaign is depicting Republican nominee Mitt Romney and his newly chosen vice-presidential running mate as "The Go Back Team" whose policies would favour the rich while sapping programs that benefit the poor and middle-class.
Mr. Obama personally took to Twitter on Sunday to warn voters that "the no. 1 thing you need to know about Paul Ryan: He's extremely conservative."
The President's tweet links to a new web site set up by the Obama campaign. It asserts that a Romney-Ryan White House would take the country "back to the failed top-down policies that crashed our economy."
The Obama campaign's depiction of the Republican ticket plays on the Romney-Ryan tagline of "America's Comeback Team."
Mr. Romney surprised many pundits on Saturday by selecting Mr. Ryan, a 42-year-old Wisconsin congressman considered to be his party's leading budget hawk, to round out the GOP ticket. While the choice left conservative commentators overjoyed, more moderate Republicans are worried it plays into the Obama campaign's hands.
Indeed, Mr. Obama's campaign team has spent months attempting to define Mr. Romney, a former corporate buy-out executive, as a cold-hearted capitalist who would slash taxes for the upper classes while gutting government investments in education and health care.
Mr. Ryan feeds into that characterization as the architect of a budget blueprint that proposes $6-trillion (U.S.) in cuts over the next decade and turning Medicare for seniors into a voucher program.
But conservatives could hardly contain themselves after hearing Mr. Romney's announcement, with some seeing the earnest Mr. Ryan as his generation's Ronald Reagan.
"The best analogy is the late 1970s when Reagan became the candidate and Democrats thought this is a real opportunity for us: 'Look at all the wild stuff he's done. He's a guy far out on the right. Easy target," commentator Charles Krauthammer said on Fox News. "And it turned out to be different. I think Ryan has that Reagan-like quality."
Mr. Ryan is considered to be a strong debater – he memorably sparred with Mr. Obama during a 2010 health-care summit – with an ever-cheerful demeanour.
Democrats "are now underestimating who they now have as an opponent," Mr. Krauthammer added.
The choice of Mr. Ryan illustrates how much Mr. Romney feels he still needs to bring the right wing of the Republican Party on board with his candidacy, as doubts about his own conservative credentials linger. It also suggests he has given up trying to make the election simply a referendum on Mr. Obama's economic record. He instead plans to go all-out in proposing a fundamental remaking of so-called entitlement programs
Still, Mr. Ryan's math has been widely criticized, since the federal government would still run deficits for almost three decades under his plan. While his blueprint proposes massive cuts, it also calls for large tax reductions for corporations and individuals.
"Ryan's extreme budget plan, which Mitt Romney has embraced, would make deep spending cuts now to pay for tax cuts for the wealthy, which would weaken the recovery and cost the economy jobs," the Obama campaign responded on Saturday.
Mr. Ryan's proposal to turn Medicare into a voucher program, giving seniors a fixed subsidy with which to purchase private insurance, would force future seniors to pay an additional $6,350 annually out of their own pockets, the Obama campaign added.
The Medicare plan, which Mr. Romney has not formally adopted, risks being a particularly tough sell in Florida, a state Republicans must win in November but which is home to a higher proportion of seniors than most.
Florida is one of four swing states Mr. Romney and his new running mate are visiting on a bus tour that began Saturday. On Sunday morning they were in North Carolina, which Mr. Obama won by only 15,000 votes in 2008 and where polls now give Mr. Romney a narrow lead.
After Florida, the Republican candidates will tour Virginia and Ohio, two more states Mr. Obama won in 2008 but which must fall into the GOP column this year for Mr. Romney to claim the White House.
All four states have strong Tea Party elements within the GOP and Mr. Romney is counting on Mr. Ryan's popularity within the movement to fire up the base and help rake in donations for the critical final stretch of the campaign.
But the choice of Mr. Ryan comes with the risk that swing voters in the centre of the spectrum will be turned off by such an ideologically-based ticket.
Republicans lost a 2011 special election in an upstate New York district shortly after Mr. Ryan's budget plan was adopted by the House of Representatives. Democrats seized on the plan to "end Medicare as we know it" to snatch the traditionally GOP seat.