The Wall Street Journal

By SARA MURRAY, COLLEEN MCCAIN NELSON and PATRICK O'CONNOR

NORFOLK, Va.—Mitt Romney picked Rep. Paul Ryan as his running mate, a decision that could spark enthusiasm for the Republican ticket among conservatives and all but ensures the election will turn to deep philosophical divisions between the two parties over spending, taxes and entitlements.

In Mr. Ryan, 42 years old, the Romney campaign gets a conservative who has spent recent years at the center of national debates about the size and scope of the federal government. With his proposals to revamp entitlement programs for future retirees and the poor, he has become a hero to conservatives and a target for liberals.

"I don't know anyone who doesn't respect his character and judgment," Mr. Romney said in front of USS Wisconsin, a World War II battleship that now is a museum and carries the name of Rep. Ryan's home state.

Mr. Romney told Beth Myers—his long-time adviser who was the head of the vice-presidential search—on Aug. 1 that he wanted Mr. Ryan as his running mate. He then called Mr. Ryan and asked to get together, according to an aide. The pick was officially announced on Mr. Romney's phone app just after 7 a.m. on Saturday.

At the Romney event, Dee and Brenda Packard, visiting Norfolk from Rigby, Idaho, praised the Ryan selection. "It's all about the budget and the economy. They are fiscal conservatives who would provide financial leadership," Mr. Packard said.

The history of vice-presidential picks suggests the choice can hurt a campaign, but rarely makes a difference on the upside. Typically, running mates are chosen to help buttress a campaign's appeal to certain parts of the country or states, or to complement a candidate's personality.

Mr. Romney's choice, by contrast, could have a more significant impact. It could go a long way to address nagging doubts about the Republican's candidacy voiced by the party's conservative wing, which has been seeking a more dramatic embrace of policy solutions to the U.S.'s long-term fiscal woes.

These kinds of big-picture budget policies, while hinted at by Mr. Romney and President Barack Obama, have been debated on the campaign only infrequently.

"I believe my record of getting things done in Congress will be a very helpful complement to Governor Romney's executive and private-sector success outside Washington," Mr. Ryan said in the prepared text for his speech released by the campaign. "We won't duck the tough issues—we will lead."

In recent days, Republicans and conservative opinion leaders have split into two groups—one urging a safe pick and the other urging a bolder and perhaps riskier choice.

The first group had pushed for figures such as Ohio Sen. Rob Portman or former Minn. Gov Tim Pawlenty, who they believe would shore up Mr. Romney's image as a steady, competent leader who can get the economy growing strongly again.

The second group had backed choices such as Mr. Ryan, as well as Gov. Bobby Jindal of Louisiana and Gov. Chris Christie of New Jersey, who are known for tough lines on fiscal matters. The idea: Picking such a candidate would tether Mr. Romney to a younger, reformist wing of the party.

"For those who thought the governor would 'play it safe' and choose someone less daring and sobering—they were wrong,'' said Don Adams, president of the Independence Hall Tea Party PAC, a Philadelphia-area group that backed Mr. Romney in the primary. "From this brave selection, we can deduce that Governor Romney takes the debt crisis so seriously that he's willing to risk his campaign on the Ryan budget plan—which seriously addresses the Federal government's disastrous and suicidal spending levels."

Meet Paul Ryan

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Brendan Hoffman/Getty Images

Paul Ryan spoke at the Peter G. Peterson Foundation's 2012 Fiscal Summit in Washington May 15.

Potential downsides of the Ryan pick include offering Democrats a single, personalized target to attack the GOP's plan for tackling the budget deficit, which has topped $1 trillion in each year of the Obama presidency. In addition, while a hero to many on the right, a congressman of 14 years and House Budget Committee chairman, Mr. Ryan remains relatively unknown outside of political and budget circles.

It is also possible Mr. Ryan's detailed prescriptions for fixing the budget could serve also to highlight the relative lack of detail so far presented by Mr. Romney.

The pick suggests a strategic rethink for Mr. Romney, whose campaign until this point seemed geared toward making the election a referendum on the president, with the GOP candidate maintaining a relatively low policy profile. The embrace of Mr. Ryan, and his budget prescriptions, turns that idea on its head.

Messrs. Ryan and Romney seemed to have genuine chemistry on the campaign trail. At one point, Mr. Ryan played an April Fool's joke on the former Massachusetts governor by introducing him to an empty room when he stumped with the presumptive nominee days before the critical Wisconsin primary earlier this year. .

During his congressional career, Mr. Ryan has written bills that would allow future retirees to invest a portion of their Social Security taxes in the stock market and transform Medicare, the health-care program for the elderly, into a system of subsidized private insurance. The congressman contends that these changes—none of which became law—are critical to avoiding the programs' insolvency.

Mr. Ryan's initial proposal to overhaul Medicare became a flash point last year when he included a version of it in his first budget blueprint as committee chairman. He has since offered a revised version that would allow younger Americans to receive standard Medicare coverage or use tax subsidies to buy private insurance.

"High unemployment, declining incomes and crushing debt isn't a new normal," Mr. Ryan said in his prepared text. "It's the result of misguided policies. And next January, our economy will begin a comeback with the Romney Plan for a Stronger Middle Class that will lead to more jobs and more take home pay for working Americans."

His colleagues in Congress haven't always warmed to his proposals. Last year, GOP leaders urged Mr. Ryan not to include versions of his Social Security changes in his initial budget blueprint.

His revised Medicare plan is the product of negotiations with Democratic Sen. Ron Wyden of Oregon, a rare act of bipartisan cooperation in a divided Congress that could confound the caricature of Mr. Ryan.

Mr. Ryan has ample experience debating the president and his allies, but the relationship wasn't always so icy. Mr. Obama initially applauded the congressman for laying out detailed policy prescriptions to balance the budget, but those cheers quickly became jeers as the president and his team savaged the proposals, at one point with Mr. Ryan in attendance, saying they would undermine long-term promises to future retirees.

Those attacks have struck a chord with older voters in some key swing states, but they have also elevated Mr. Ryan to the national stage. After spending almost two years parrying these attacks from Democrats in Congress and in his numerous TV news-show appearances, Mr. Ryan appears well prepared to combat this criticism on the campaign trail.

A fifth-generation native of Janesville, Wis., Mr. Ryan adds stronger Midwestern roots to a ticket already topped by the son of a former Michigan governor. The Romney campaign is looking to flip states Mr. Obama won, from Iowa to Pennsylvania. He also offers the ticket a youthful face.

While Mr. Ryan may hold strong appeal for outside-the-Beltway tea-party types, he has spent much of his professional life in the nation's capital.

In college, Mr. Ryan worked as an intern for former Wisconsin Sen. Bob Kasten. After earning a degree in economics and political science from Miami University in Oxford, Ohio, he returned to Washington as an aide to the Republican senator, helping to pay the bills with stints as a personal trainer and as a waiter at a Mexican restaurant a few blocks from the Capitol.

When Mr. Kasten lost, Mr. Ryan signed on with Empower America, a free-market think tank led by former New York Rep. Jack Kemp. The two men eventually formed a political bond, and Mr. Ryan often credits the former congressman as a mentor.

This isn't Mr. Ryan's first brush with presidential politics: When former Kansas Sen. Bob Dole named Mr. Kemp as his running mate in 1996, Mr. Ryan signed on as a speechwriter to the vice-presidential nominee.

Mr. Ryan remains a fitness enthusiast, who leads regular morning workouts for a band of younger, mostly Republican lawmakers. He is also an avid hunter who used to grow a beard during deer season to mask his scent.

Speculation had been building that the announcement was close. The Romney campaign had previously said it would come before the Republican National Convention kicks off Aug. 27 in Tampa, Fla., but the candidate and his aides had offered few other clues. Most recent presidential nominees have announced their selection in the week before their party's national convention.

Mr. Romney is flanked on the bus tour by much of his inner circle, including Beth Myers, who led the vice-presidential search committee, his longtime adviser Eric Fehrnstrom and Bob White, one of the candidate's closest friends.

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—Janet Hook contributed to this article.