Republican Vice Presidential candidate, Paul Ryan (L) and Vice President Joe Biden

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, reports Reuters.

"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, who warned that "maybe there will be some dishonesty," from the Republican.

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.

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.