When it came down to it, Barack Obama chose safe rather than bold, experience rather than change.

With his long record, Sen. Joe Biden, D-Del., will help reassure some voters nervous about Obama's lack of experience on foreign affairs, much as Dick Cheney did when he was chosen as the young George W. Bush's running mate.

And with one of the thinnest wallets in the Senate, Biden also could help reach out to working class voters who've been cool to Obama in places such as Ohio and West Virginia.

And as a Roman Catholic, he could speak to that swing voting bloc in key states such as Florida, Pennsylvania and Wisconsin.

Sleeves rolled up, Biden bounded onto an outdoor stage in Springfield, Ill., Saturday and kicked off his campaign as Obama's running mate with an emotional appeal to blue-collar voters and a blistering attack on Republican candidate Sen. John McCain.

Obama spoke first Saturday in a carefully choreographed event outside the Old State Capitol, the stately limestone edifice where Abraham Lincoln once worked, and where Obama, a first-term senator from Illinois, launched his unlikely White House campaign 19 months ago.

"Joe won't just make a good vice president – he will make a great one," Obama promised the crowd, which police estimated at 35,000.

Overall, Biden looks familiar and safe as Obama's choice for vice president. That could undercut Obama's message of bold new leadership.

But it also could help Obama look careful and deliberate at the very time Republicans want to cast him as a dangerous, radical neophyte.

That may not be all bad, especially at a time when Russian troops are in Georgia, Pakistan is changing leaders and Americans are again thinking about who will have his hand on the levers of power in national security and international affairs.

Obama needs to assure voters that he can handle a crisis, the same concern that former Democratic rival Hillary Rodham Clinton raised when she aired an ad asking who voters want in the White House when a crisis erupts at 3 a.m.

A recent Zogby poll found, for example, that voters McCain to handle such situations. Another found that the recent fighting between Russia and Georgia had voters leaning heavily toward McCain as more qualified to handle a resurgent Russia.

Obama also wants to attract more support from Roman Catholics, a key swing group closely divided between McCain and Obama.

Catholics account for about one in four voters nationwide, and a higher concentration in such political battleground states as Florida, New Hampshire, New Mexico, Pennsylvania and Wisconsin.

And Biden – a son of blue-collar workers and a man whose net worth falls short of $150,000 – can speak to white, working class voters in a way that Obama might not.

Beyond those niche appeals, Biden likely will do well in one of the key roles for a running mate – attacking the other ticket. Most presidential candidates want to take the high road themselves while their No. 2 hits hard – a political good cop-bad cop act.

"He is a tough attack dog," said Sherry Bebitch Jeffe, a political scientist at the University of Southern California.

After Obama introduced Biden Saturday, Biden gave a speech filled with jabs at McCain. He mocked McCain's inability in an interview last week to recall how many houses he and his wife, Cindy, an heiress whose net worth is estimated at up to $100 million, actually own.

While other families sit at the kitchen table and worry about paying bills, Biden said McCain faces a choice. "He'll have to figure out which of the seven kitchen tables to sit at," he said.

In one of the harshest criticisms the Democrats have leveled at McCain, Biden suggested he has lost his moral compass in his drive for the White House.

"I must tell you, frankly, I've been disappointed in my friend John McCain, who gave in to the right wing of his party and yielded to the very Swift boat politics that he once so deplored," he said.

As polls show the race tightening, Democrats increasingly have been questioning whether Obama can play the game of brass-knuckle politics against McCain. Biden, however, left no doubt he's comfortable going for the jugular.

Biden does carry some risks.

First, of course, is his image as an insider. Second is a tendency to off-the-cuff remarks that can appear impolitic, such as calling Obama the first "clean" black candidate for president.

Referring to Biden in Springfield, Obama said, "He's that unique public servant who is at home in a bar in Cedar Rapids and the corridors of the Capitol; in the VFW hall in Concord, and at the center of an international crisis. That's because he is still that scrappy kid from Scranton who beat the odds; the dedicated family man and committed Catholic who knows every conductor on that Amtrak train to Wilmington."

"That's their way of stressing his blue-collar roots and saying he's not part of the Beltway crowd," Jeffe said.

On the other hand, she said, his tendency to make blunt, embarrassing comments could be turned to his advantage by making him appear candid and honest.

"That could position him as a maverick," Jeffe said. "For the average voter, it could be a positive. It takes him out of the stereotype of the smooth Washington insider."

One that will be harder to counter is the record of criticisms Biden leveled at Obama during the primaries. In one, for example, Biden called Obama too inexperienced, a clip the McCain camp rushed into TV commercials by midday Saturday.

Biden responded Saturday by saying he'd seen Obama grow in the crucible of a presidential campaign in which "you're tested and challenged every single day."

"Over the past 18 months, I've watched Barack meet those challenges with judgment, intelligence and steel in his spine," Biden said.

Los Angeles Times, Associated Press and New York Times contributed to this report.