WASHINGTON - US Republican Party's presumed presidential nominee Mitt Romney on Saturday defied perception of him as a guy who plays it safe by choosing Paul Ryan - a young, wonky US Representative from Wisconsin, a state in the Midwest - as his running mate.

Being the architect behind a controversial Congress budget plan that slashes spending, cuts taxes and privatizes parts of Medicare, Ryan puts the ideological differences between Republicans and Democrats on government spending and ways to grow the economy squarely back to the presidential debate.

Romney's pick of Paul Ryan could carry both benefits and pitfalls.

"The selection of Rep. Ryan has both conventional and unconventional aspects to it," Joel Goldstein, a Saint Louis University professor who is a leading expert on US Vice Presidency, told Xinhua Saturday.

Goldstein said just like George H.W. Bush selected Dan Quayle, Bob Dole picked Jack Kemp and John McCain chose Sarah Palin, Romney, a perceived moderate Republican, chose a running mate from the right wing of the party.

"Like other governors or former governors since 1952, Gov Romney chose a running mate with experience in the national government in Washington, DC" added Goldstein. Romney used to serve as governor of Massachusetts from 2003 to 2007.

In addition to complementing Romney on a range of issues, Ryan brings with him the "Path to Prosperity," the so-called Ryan budget, which is a budget blueprint drawn by Ryan that cuts spending as well as taxes, overturns the White House's healthcare law and replaces parts of Medicare with government subsidized private insurance plans.

"It's unusual in that Gov. Romney has embraced Rep. Ryan's controversial plan regarding cutting taxes and cutting domestic spending," said Goldstein, as the Democrats are sure to target the Ryan budget in their attacks.

In a written statement, Jim Messina, President Barack Obama's campaign manager, criticized Ryan as "the architect of the radical Republican House budget" which "proposed an additional $250,000 tax cut for millionaires and deep cuts in education."

"With Mitt Romney's support, Ryan would end Medicare as we know it and slash the investments we need to keep our economy growing - all while cutting taxes for those at the very top," said Messina in an email to supporters.

The Romney campaign, however, has decided picking Ryan's benefits outweigh pitfalls.

"Going big has risks, but fewer than going small. Now this is a race about what the future's going to look like," said a Romney adviser, who reckoned that Romney "isn't thinking about Ohio or the Hispanic vote. He's thinking: I'm going to be president. Who's going to help me succeed?"

A chance of course for the race

Romney has been pummeled recently by Obama camp's negative ads, and polls show the blitz has taken its toll. By picking Ryan, Romney has taken back the initiative, and could potentially re-write the election's rhetoric.

"Romney's choice of Paul Ryan tells us a lot about his confidence," said Karlyn Bowman, a public opinion expert with the American Enterprise Institute. "People vote for the top of the ticket in presidential contests. It's important not to do any harm with a VP pick. Romney hasn't hurt his chances and Paul Ryan may have helped at the margins," said Bowman.

The pick is sure to excite conservatives. Rick Santorum, Newt Gingrich and Michele Bachmann all praised the selection. The Tea Party Patriots, in a statement, said by selecting Ryan, Romney made it clear that he has "accepted the Tea Party Patriots values of fiscal responsibility, limited government and free markets as the best course of action for economic recovery."

In an election where undecided voters are few, keeping the base excited is crucial.

Romney's VP pick has triggered off some negative reactions from the Obama campaign which has already labeled the Romney/Ryan ticket as the "Go Back Team," and rolled out web pages attacking Ryan's budget plan. Democratic leaning groups are also joining the attacks.

As Obama campaign team has been focusing on Romney's tax returns, Bain Capital records and dressage horse in the past weeks, the American election race is likely to take a turn for the basics and the fundamental differences between the Republicans and the Democrats on spending, taxes and entitlements.