NORFOLK, Virginia (AP) ― Republican Mitt Romney introduced Wisconsin Congressman Paul Ryan as his vice presidential running mate on Saturday, turning to an ardent conservative and budget-cutting specialist to shore up support for his candidacy among the party’s conservative base.

The party establishment, rank-and-file conservatives and small-government, anti-tax tea party groups all cheered the pick made by Romney. As chairman of the House Budget Committee, Ryan is the architect of a deeply conservative and intensely controversial long-term budget plan to cut trillions in federal spending and is widely viewed by Republican lawmakers as an intellectual leader within the party.

Romney chose Ryan as a means of mollifying the Republican right wing which has shown only modest enthusiasm for his candidacy, given Romney’s past record as a moderate during his term as governor of Democratic-leaning Massachusetts less than a decade ago. Ryan, a Roman Catholic, also enjoys support among social conservatives for his staunch opposition to abortion and gay marriage.

Ryan joins the campaign against President Barack Obama in a race defined from the beginning by a weak economy and high unemployment, measured most recently at 8.3 percent in July. Even so, recent national polls as well as surveys in several battleground states indicate a narrow advantage for Obama with less than three months remaining before the Nov. 6 election.

Romney needs to repair his image after a summer filled with political gaffes, especially during a trip abroad, and the incessant drumbeat of negative advertising by Obama’s campaign which has portrayed the Republican as an out-of-touch multi-millionaire who has been evasive about releasing his tax records.

Ryan came out swinging early Saturday, vowing to defeat Obama and repair the ailing U.S. economy.

America is “a nation facing debt, doubt and despair,” and a transformative change in leadership is vital, Ryan declared to a flag-waving crowd in the first moments after Romney introduced him as his partner for the campaign.

“Regrettably, President Obama has become part of the problem ... and Mitt Romney is the solution” to an economy that has yet to make a strong recovery from the worst recession in decades, said the seven-term congressman, who at 42 is a generation younger than Romney, 65.

The two Republican ticket mates basked in the cheers of supporters in a made-for-television debut. “I did not make a mistake with this guy,” Romney exulted.

Romney declared that in the campaign to come, Republicans will present economic solutions “that are bold, specific and achievable. ... We offer our commitment to help create 12 million new jobs and to bring better take-home pay to middle class families.”

Obama’s campaign didn’t wait long to respond. It criticized the budget blueprints Ryan has authored, particularly his recommendations to fundamentally remake Medicare, the national health insurance program for Americans age 65 and older, and cut $5.3 trillion in government spending over the coming decade.

“The architect of the radical Republican House budget, Ryan, like Romney, proposed an additional $250,000 tax cut for millionaires, and deep cuts in education,” Jim Messina, the president’s campaign manager, said in a written statement.

Democrats believe Romney’s choice of Ryan could boost their fortunes by linking the Republican candidate to unpopular congressional Republicans. Democratic leaders made clear that Romney would be forced to adhere to the principles laid out in the House Republican budget ― authored by Ryan ― which they said would undermine entitlement programs crucial to middle-class families and seniors.

While Romney’s pick unified Republicans, the impact in pivotal battleground states such as Florida, Iowa and Pennsylvania was an open question. All are home to large numbers of seniors whose reaction to Ryan’s prescription for Medicare is certain to be tested by Democrats.

Ryan’s selection as well as Romney’s own nomination will be ratified by delegates to the Republican National Convention that begins on Aug. 27 in Tampa, Florida.

Obama and Vice President Joe Biden will be nominated for a second term at the Democratic convention the following week in Charlotte, North Carolina. The vice president called Ryan to congratulate him on his selection, the president’s campaign said.

The Republican ticket made its debut at a naval museum in Norfolk, Virginia, opening stop of a bus tour through four battleground states in as many days. A trip to Ryan’s home state of Wisconsin was added to previously scheduled appearances in Virginia, North Carolina, Florida and Ohio.

Having Ryan on the ticket could help Romney become more competitive in Wisconsin, a state Obama won handily four years ago in the state-by-state race for the presidency, but that could be much tighter this November. Ryan represents a district in the southeast of the state.

The battleship USS Wisconsin, berthed at the museum, provided a bunting-draped backdrop, a symbol of U.S. military strength as well as an obvious reference to Ryan’s home state.

First Romney, then Ryan, jogged down the ship’s gangplank to the cheers of hundreds and the stirring soundtrack from the movie “Air Force One.”

As his family came on stage, Ryan knelt to embrace his daughter, Liza, 10, and sons Charles, 8, and Sam. 7, before kissing his wife, Janna.

Later, the two held rallies before enthusiastic crowds in Ashland and Manassas, Virginia.

In turning to Ryan, Romney bypassed other potential running mates without the Wisconsin lawmaker’s following among rank-and-file conservatives, including Ohio Sen. Rob Portman and former Minnesota Gov. Tim Pawlenty, who were both viewed as safer picks.

Republican officials said Romney had spoken with both men.

In the House of Representatives, Ryan is the primary author of conservative tax and spending blueprints that the tea party-infused Republican majority approved over vociferous Democratic opposition in 2011 and again in 2012. The plan failed to gain approval in the Democratic-controlled Senate.

It envisions transforming Medicare into a program in which future seniors would receive government checks that they could use to purchase health insurance from private companies. Under the current program, the government directly pays doctors, hospitals and other health care providers. Obama contends the plan would end up costing Medicare beneficiaries more than $6,000 a year.

Ryan and other supporters say the change is needed to prevent the program from financial calamity.

Other elements of the budget plan would cut projected spending for Medicaid, the government plan that provides health care for the poor, as well as for vouchers to purchase food, student loans and other social programs that Obama and Democrats have pledged to defend.

It also envisions a far reaching overhaul of the tax code of the sort Romney has promised.

Ryan has worked in Washington for much of his adult life, a contrast to Romney, who frequently emphasizes his experience in business. He is also well-known for his fiendish physical fitness workouts.

Ryan worked as an aide in Congress, and also was a speechwriter for U.S. Rep. Jack Kemp, the party’s 1996 vice presidential candidate who had been one of the driving forces behind across-the-board tax cuts that were at the heart of Ronald Reagan’s winning presidential campaign in 1980.