Rep. Paul Ryan, R-Wis. (File)

NORFOLK, Va. (August 11, 2012)--Republican presidential challenger Mitt Romney appeared alongside his running mate, Wisconsin Rep. Paul Ryan Saturday morning, calling Ryan a man of "great steadiness" and "unquestioned integrity."

The former Massachusetts governor said Ryan is a "shining exception" in a political world of pettiness.

The two appeared together for the first time as the Republican presidential ticket on Saturday morning in Virginia before a group of cheering supporters while standing on the USS Wisconsin, a retired World War II battleship.

Just hours after his campaign confirmed Ryan as his selection, Romney says Ryan won't demonize his opponents.

Romney said that Democrats may disagree with Ryan's policies, but he doesn't know anyone who doesn't respect his character and judgment.

Romney stumbled as he introduced his running mate, however, mistakenly introducing Ryan as the next president of the United States, rather than as the next vice president.

A sheepish Romney puts arms around Ryan and clarified his mistake before Ryan took the microphone.

Romney said he makes a mistake every once in a while, but said he didn't make a mistake with his selection of Ryan.

Ryan is chairman of the House Budget Committee, and primary author of conservative budget plan that would remake Medicare and cut trillions in federal spending.

The Republican-controlled Congress passed Ryan's tax and spending blueprints over vociferous Democratic opposition in 2011 and again in 2012.

In a written statement, Romney's campaign said Ryan has worked in Congress to "eliminate the federal deficit, reform the tax code and preserve entitlements for future generations."

Former President George W. Bush praised the choice in a brief statement Saturday.

"This is a strong pick. Governor Romney is serious about confronting the long-term challenges facing America, and Paul Ryan will help him solve the difficult issues that must be addressed for future generations, he said."

Texas Gov. Rick Perry, who dropped out of the GOP presidential race, called Ryan a “conservative budget hawk” and said in a statement issued Saturday that the choice underscores Romney's "commitment to downsizing Washington, fixing our economy and restoring American job creation."

His statement called Ryan an exciting choice who will "energize economic voters, young voters and blue collar voters" while solidifying the Republican Party's commitment to fiscal responsibility.

Former Minnesota Gov. Tim Pawlenty, who was passed over in favor of Ryan, said he’s excited by Romney’s choice.

In a statement, Pawlenty calls Ryan a "respected leader and a bold thinker" about changes needed for the country.

He also says Ryan's roots in Wisconsin will help Romney win that key swing state.

He says he'll do all he can to help Romney win the election.

President Barack Obama's campaign was quick to respond to the announcement, saying that Romney's selection of Ryan as his running mate shows a commitment to "budget-busting tax cuts" for the wealthy and "greater burdens" on the middle class and seniors.

Obama campaign manager Jim Messina called Ryan is the "architect of the radical Republican House budget" proposal and says the plan "would end Medicare as we know it."

The Obama campaign said Saturday the Republican ticket would return the nation to "reckless Bush economic policies that exploded our deficit and crashed our economy."

Democrats are expected to seize upon Ryan's authorship of a House-backed budget plan that would curb overall entitlement spending and changes Medicare into a voucher-like system.