When I followed Sen. Joe Biden (D-Del.) through South Carolina for a day late last fall, I was working on a story about second-tier presidential candidates. I didn't predict that less than a year later, Biden would become a candidate for second-in-command.

After a long day that ended near the children's section of the Happy Bookseller in Columbia, S.C., Biden talked to every man, woman, and child out of about two dozen who showed up for his book-signing event.

Before he realized I was a reporter, Biden threw an arm around my shoulder, brandished his wide grin, and thanked me for staying for so long. When I told him I was a journalist, he dropped the arm, but kept the grin. He was happy for the press.

As he emerges as Sen. Barack Obama's running mate, Biden, 65, will have more press than he's ever known in his 35 years in Congress. If he carries himself the way he did on the campaign trail last fall, Democrats will have plenty of reasons to welcome Biden-and worry about him.

First, why they'll welcome him: When Biden slipped through the back entrance of the tiny Democratic headquarters in downtown Rock Hill, S.C., that crisp morning last year, he squeezed through the crowd and stood square in the middle. Not quite a Connecticut Yankee in King Arthur's Court, he was nonetheless a northern liberal in a conservative Southern town, and these Democrats were eating out of his hand.

Biden was funny and personable, and had a way of making himself sound like the most logical choice for the presidency, even if everyone knew he'd never make it. He worked the crowd like these were his constituents, and connected on an individual level the way Obama does on a grand scale. That could help.

A few hours later, when Biden strode through the marble-floored halls of the Capitol building in Columbia, staffers and tourists seemed to recognize him. Even if some couldn't quite place him, they knew they knew him. Next to a relatively unknown quantity like Obama, that could help, too.

During the ensuing press conference, flanked by Revolutionary War portraits, Biden talked about foreign policy with ease and confidence, as well as blatant scorn for President Bush. (Though he originally voted for authorizing the Iraq war, he later opposed the troop surge.) As chair of the Senate Foreign Relations Committee, Biden brings foreign policy credentials that Sen. John McCain blasts Obama for not possessing. Another plus.

But here's why Democrats should worry: When it comes to foreign policy, McCain isn't the only one who has blasted Obama. So has Biden. Last year, Biden warned against Obama's lack of experience: "If the Democrats think we're going to be able to nominate someone who can win without that person being able to table unimpeachable credentials on national security and foreign policy, I think we're making a tragic mistake."

Biden also criticized Obama for voting against a war-funding measure in Congress. Speaking of his son, Beau, who will soon deploy to Iraq with the Delaware National Guard, Biden said: "There's no political point worth my son's life."

Biden's recognition factor could work against Obama, too: Obama's mantra of "change" could deflate a little under Biden's six terms in Congress. And Democrats who were hoping for a moderate pick to attract independent voters won't find much solace in Biden's solidly liberal voting record.

Finally, Biden's loquacious ways could eventually haunt Obama. The writer of Proverbs warns against "abundance of words" for good reason, and the famously verbose Biden sometimes gets himself in trouble. Commenting on the large population of Indian immigrants in Delaware, Biden once said: "You cannot go to a 7/11 or a Dunkin' Donuts unless you have a slight Indian accent."

When he announced his bid for the presidency last year, Biden called Obama "the first mainstream African American [candidate] who is articulate and clean and a nice-looking guy." (He quickly clarified his comments, and Obama understood.)

And Biden's verbosity won't provide much balance for Obama's oft-flowery speech. Many pundits declared McCain the winner of last week's Civic Forum on the Presidency at Saddleback Church with pastor Rick Warren largely on this point: McCain was succinct. Obama wasn't.

Biden was characteristically candid with me on that fall day last year. Standing near the pop-up books, the then-presidential candidate reminded me that Democrats viewed Howard Dean as the inevitable nominee before his candidacy imploded overnight in 2004.

Given Obama's recent aura of invincibility in some quarters, Biden's commentary seems a little ominous today: "He was the anointed candidate," Biden said of Dean last fall. "And look what happened. This thing is wide open."