NORFOLK, Va. -– Mitt Romney will announce Rep. Paul Ryan (R-Wis.) as his running mate on Saturday, according to two sources with knowledge of the decision.

In a press release issued Saturday morning, the Romney campaign confirmed the decision, calling the duo "America's Comeback Team."

Ryan is a bold pick who will energize the Republican Party, but putting him on the ticket is fraught with risk and instantly puts Ryan's budget plan front and center in the 2012 campaign.

Romney will announce his choice in Norfolk on Saturday morning at the beginning of a four-day bus tour through key battleground states, the campaign said Friday night. The Weekly Standard reported earlier Friday that Wisconsin Gov. Scott Walker has been asked to be ready to make the case for Ryan beginning Saturday.

Romney's alliance with the 42-year old Ryan has become the most dramatic development of the 2012 presidential campaign. Romney had been presumed for much of the last few months to be set on a safe pick, such as Sen. Rob Portman (R-Ohio), or former Minnesota Gov. Tim Pawlenty.

But now, Romney, who is 23 years older than Ryan, will signal that he is willing to roll the dice. President Barack Obama's reelection campaign and Democratic political groups have been eager for Romney to pick Ryan, the architect of plans to slash government spending and overhaul entitlement programs that Democrats believe are political losers.

Both liberals and conservatives will be thrilled with Romney's choice.

Conservatives believe Ryan is one of the brightest, best young faces and minds who can cheerfully articulate a case for limited government while simultaneously arguing that a less expansive bureaucracy and a revamped entitlement system is the best way to preserve government aid and benefits for the poor, indigent and elderly.

Ryan's budget and his proposed changes to programs like Medicare will now be central issues that drive the presidential campaign for the remaining three months. It is one way for Romney to turn a campaign that has turned ugly and personal, often to his detriment, into a heated debate over policy.

The battle to define Ryan and his reform plan will set off a messaging war between Democrats and Republicans, the likes of which has rarely been seen.

If Romney were to win with Ryan on the ticket, he would have a mandate to make sweeping changes not only to the size of government, but to programs like Medicare and Medicaid that are products of former President Lyndon Johnson's Great Society program.

For conservatives, putting Ryan front and center will satisfy their desire to have a full-throated debate about the entire spectrum of issues that they feel are most pressing: the size of the federal government, the government's role in people's lives, the impact of the national debt on the middle class, and how to maintain a social safety net without creating a "culture of dependency" in which too many citizens receive government benefits.

For liberals, Ryan represents a chance to not just defeat Romney, but an opportunity to discredit, on the biggest stage in politics, the most wide-ranging expression of conservatives' governing principles put forward in recent political memory. Liberals will say that Romney and Ryan want to cut government spending in a way that will hurt the economic recovery and cut assistance to those who need it. Obama himself has already attacked Romney for wanting to "turn Medicare into a voucher program," a reference to Ryan's original proposal for Medicare.

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