By Sam Youngman
ST. PETERSBURG, Florida (Reuters) - Republican Congressman Paul Ryan is a changed man.
Presidential candidate Mitt Romney's running mate made a name for himself as a bold fiscal crusader, willing to make big, unpopular cuts to entitlements to get U.S. finances in order.
But since Romney tapped him in August to join his campaign, the vice presidential candidate has become more prudent, avoiding detailed discussion of his budget plan and earning the nickname "mini-Mitt" for displaying a cautious streak like his boss.
For Vice President Joe Biden, a major question heading into his debate with Ryan in Kentucky on Thursday is "a choice of which Ryan we're going to see," a Biden adviser said.
Instead of promoting his own budget plan, which includes caps on future Medicare spending, Ryan is talking up Romney's more voter-friendly version, which has no spending limits, at campaign events.
"The vice president has been studying up on (Ryan's) real positions and is prepared to call him out on his actual positions," said the adviser.
The adviser warned that Biden will be on the lookout for what he called "dishonesty" by Ryan, part of the Obama campaign's strategy to accuse its Republican rivals of bending the facts in the final stretch of the election campaign.
The stakes are high for Biden, who is charged with righting a listing ship after President Barack Obama's disastrous first debate against Romney in Denver last week, which lost him the momentum in polls ahead of the November 6 election.
Democrats have targeted Ryan's budget, a severe series of spending cuts, as proof that he would hurt seniors and the middle class.
One top Republican strategist said the best way for Biden to battle his opponent is to tease out the "wonky" Ryan, the congressman who loves mind-numbing fiscal details.
"If I was prepping against Ryan, I would be looking for issues that Romney and Ryan disagree on and try and pull out Ryan the wonk, as opposed to Ryan the running mate," the strategist said.
That would turn off television viewers not used to detailed policy arguments, and could give Biden a chance to paint the Republican team as holding different positions on Medicare.
The Romney campaign has worked overtime to emphasize that House Budget Committee chairman Ryan has fallen in line with the presidential candidate on fiscal issues.
"You have to remember this is a Romney-Ryan ticket, and there's one presidential candidate, there's one person at the top of the ticket," Romney spokesman Kevin Madden told reporters on Tuesday.
Ryan met staff to discuss the debate and other issues at a hotel in St. Petersburg, Florida on Wednesday morning before flying to Kentucky later in the day.
NO RYAN DOCTRINE
An image of Ryan as a congenial Midwesterner rather than a congressional budget hawk has been enhanced on the campaign trail, where he has worked to build a reputation for an easy manner with voters.
Much was made in the media of Ryan cutting short an interview this week with a local television reporter whose questions he did not like, but the Wisconsin congressman was in good spirits immediately after the interview, and did not storm off as was suggested.
Economic issues aside, Ryan is clearly taking his lead from Romney on foreign policy, a weak spot for the 42-year-old congressman against Biden, who spent more than 10 years on the Senate Foreign Relations Committee.
In Ohio on Monday, Ryan echoed much of the language and themes that the former Massachusetts governor laid out in an attack on Obama's handling of world events during a speech at the Virginia Military Institute.
"The president is not offering the kind of spirited and principled leadership we need to create jobs here at home or to keep us safe," Ryan said.
At a rally, he pressed home criticism of Obama over the killing of four Americans in Libya, a favorite foreign policy attack line of Romney.
Ryan told voters to just turn on their televisions: "You will likely see the failures of the Obama foreign policy unfolding before our eyes," Ryan said. "You see if you look around the world, what we are witnessing is the unraveling of the Obama foreign policy."
Leading up to Thursday's debate, Ryan retreated to Florida to prepare, spending Tuesday morning focused on policy briefings before switching to debate prep.
Ryan aides in recent days have begun the typical campaign ritual of playing up your opponent before a debate, portraying Biden as a seasoned professional.
"Vice President Biden has done 18 presidential or VP debates over the years - 14 in 2008," said one Ryan aide. "He's always a focused debater. It's not a setting in which he makes gaffes."
Brendan Buck, a Ryan spokesman, noted that Thursday night will be Ryan's "first time on the big stage."
"After the president's performance last week, we know Joe Biden will (be) coming at us like a cannonball," Buck said.
(Reporting By Sam Youngman; editing by Alistair Bell and David Storey)