Mitt Romney could have said almost anything to a buoyant crowd ready to welcome his new running mate and it would have been OK. But flubbing Paul Ryan's big intro evoked a moment of "Say what?" uncertainty.

About 1,000 people had queued in long lines starting before daylight to be the first to hail the Wisconsin congressman who became a conservative hero for championing deep spending cuts.

People beamed, leaning forward, standing on tiptoes, craning their necks as Romney set up the most anticipated debut of his candidacy.

Then Romney says, "… the next president of the United States, Paul Ryan."

Snickers and puzzled expressions muted a building ovation for a heartbeat or two. But then came a throaty outburst, nearly drowned out by heroic movie-theme music loud enough to be felt through the pavement, as Ryan bounded down the bunting-draped steps from the USS Wisconsin, gave Romney a quick hug and joined him in waving to a crowd aflutter with flags.

After Ryan had already launched into his speech about unabashed budgetary austerity, traditional values and the failures of President Barack Obama's Democratic White House, Romney stepped back onstage to smilingly correct his gaffe.

"I did not make a mistake with this guy," Romney told the crowd, and it was quickly forgotten.

After all, Obama made the same flub four years ago introducing his running mate and corrected himself instantly: "So let me introduce to you, the next president —the next vice president — of the United States of America, Joe Biden!"

Ryan's conservative credentials

Ryan is the architect of a deeply conservative and intensely controversial long-term budget plan to cut trillions in federal spending, and his conservative credentials are highly regarded by fellow Republicans who control the House of Representatives.

Romney chose Ryan as a means of mollifying the Republican right wing which has shown only modest enthusiasm for his candidacy, given the former Massachusetts governor's history, until his presidential campaign, of acting from a moderate political philosophy.

Ryan joins the ticket in a race defined from the beginning by a weak economy and high unemployment, measured most recently at 8.3 per cent in July. Even so, recent national polls as well as surveys in several battleground states indicate a narrow advantage for Obama.

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 apparatus which has portrayed the Republican candidate as an out-of-touch multi-millionaire who is evasive about releasing his tax records. In combination, those realities have harmed the Republican's campaign momentum and seen him lose ground to Obama.

Ryan came out swinging early Saturday, blaming Obama for the country's sluggish economy.

"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, he said.

In the campaign to come, Republicans will present economic solutions "that are bold, specific and achievable," Romney said. "We offer our commitment to create 12 million new jobs and bring better take home pay to middle class families."

The ticket-mates made their first joint appearance at a naval museum, in front of the battleship USS Wisconsin, the initial stop of a bus tour that will take them through four battleground states — Virginia, North Carolina, Florida and Ohio — in as many days. It seemed likely a stop in Ryan's home state would be added to the schedule.

First Romney, then Ryan, a generation younger than his patron, jogged down the ship's gangplank to the cheers of hundreds and the stirring soundtrack from the movie Air Force One.

Democrats ready to pounce

Democrats also had hoped for the Ryan selection, believing they could boost their fortunes by pinning on Romney what they see as an unpopular budget plan that calls for deep cuts in government spending and a major overhaul of entitlement programs.

Mitt Romney, left, was widely expected to pick Wisconsin congressman Paul Ryan, right, to be his running mate. He announced the decision on Saturday morning in Norfolk, Va. (M. Spencer Green/Associated Press)

President Barack Obama met with top advisers Saturday at his campaign headquarters shortly after arriving in Chicago for a series of birthday-themed fundraisers scheduled for Sunday. The president did not publicly comment on Ryan's selection and aides described the headquarters stop as a typical weekly meeting.

Less than two hours after Romney introduced Ryan as his running mate, the Obama campaign released a 90-second Web video showing footage of the men appearing together. The ad calls Ryan the "mastermind behind the extreme GOP budget plan" and includes an audio clip of Romney saying earlier this year that it would be "marvelous" if the Senate were to adopt the Ryan budget. The ad ends with this tagline: "Mitt Romney and Paul Ryan: Back to the failed top-down policies that crashed our economy."

Obama's campaign manager, Jim Messina, said in a statement that Romney had "chosen a leader of the House Republicans who shares his commitment to the flawed theory that new budget-busting tax cuts for the wealthy, while placing greater burdens on the middle class and seniors, will somehow deliver a stronger economy."

At 42, Ryan is a generation younger than the 65-year-old Romney.

Ryan is chairman of the House budget committee and 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 — the national health insurance program for Americans age 65 and older — 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 food stamps, student loans and other social programs that Obama and Democrats have pledged to defend. Food stamps allow the poor to buy food at a discount.

In all, it projected spending cuts of $5.3 trillion over a decade, and cut future projected deficits substantially. It also envisions a far-reaching overhaul of the tax code of the sort Romney has promised.

Ryan viewed as risky selection

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 recent days, conservative pundits and some mainstream Republicans have been urging Romney to choose Ryan in large part because of his authorship of the House-backed budget plan. Ryan, a Roman Catholic, also enjoys support among social conservatives for his staunch opposition to abortion.

Ryan has worked in Washington for much of his adult life, a contrast to Romney, who frequently emphasizes his experience in business.

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.

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 Joseph Biden will be nominated for a second term at the Democratic convention the following week in Charlotte, North Carolina.

Appear comfortable together

Romney and Ryan appeared unusually comfortable with each other when they campaigned together earlier in the year. The former governor eagerly shared the microphone with the younger man and they shared hamburgers at a fast food restaurant.

Romney was the subject of an April Fools prank in which Ryan played a role. Romney showed up at a supposed campaign event where he heard Ryan calling him "the next president of the United States" — only to find the room nearly empty.

Republican National Committee finance chairman Ron Weiser said Friday night that Ryan's selection would help Romney win Wisconsin and its 10 electoral votes in the fall. The state typically supports Democrats in presidential contests, and Obama won it handily four years ago.