House Speaker Nancy Pelosi, D-Calif., said Biden offered "the full package." She said he "has challenged the status quo. And he's even criticized Senator Obama, so it's a tribute to Senator Obama that he's not just choosing a yes man but a person who will speak what he believes."
Fresh from announcing his running mate, Obama was resuming pre-convention campaigning with a scheduled stop in Wisconsin in the run-up to accepting the Democratic nomination for president. He was also campaigning in Iowa, Missouri and Montana before the nomination becomes his Thursday in Denver.
Also Sunday, the party's credentials committee was poised to restore full voting rights at the convention to delegates from Florida and Michigan, initially stripped of all delegates for holding their primaries too early. With his nomination assured, Obama sought the show of unity to shore up support in those two important states.
Since Biden's selection, the McCain campaign has come out with two campaign ads addressing the Democratic candidate's choice of a running mate.
The latest ad, released by the campaign early Sunday, features clips of Clinton during the primary battle saying critical things about Obama, including, "Senator Obama's campaign has become increasingly negative."
A voiceover announcer says, "She won millions of votes but isn't on the ticket. Why? For speaking the truth."
Axelrod said Obama "has a high regard for Senator Clinton. She's going to be an important voice in this campaign, she's going to be an important voice in moving this country forward in the next administration. But he felt Senator Biden would be the best fit for him at this time."
In addition to Biden's long resume, including his chairmanship of the Senate Foreign Relations Committee, "he's an independent guy who will tell the president what he needs to know even if he doesn't want to hear it," Axelrod said.
Caroline Kennedy, a member of Obama's search team, said "Joe Biden was absolutely the best" of the choices under review. She declined to say whether Clinton was screened, but called her a "tremendous groundbreaking figure. Everyone admires her greatly. He is going to need her in the Senate."
Two potential swing-state governors - Virginia's Tim Kaine and Colorado's Bill Ritter - welcomed Biden's selection.
Kaine, who had been on Obama's short list for a running mate, said Obama and Biden were "a good team personality-wise. They complement each other well. I think you're going to see them really enjoying being out on the trail together."
Ritter said Obama and Biden together would help the ticket, particularly with independent voters in the West.
Biden returned to Delaware after their first joint appearance Saturday in Springfield, Ill., where Obama had begun his campaign in February 2007. Obama headed to Eau Claire, Wis., a city of 65,000 about 85 miles east of St. Paul, Minn., site of the Republican convention next month. He was expected to discuss ways to stimulate the economy and help middle-class families.
Biden attended church near his home in Greenville, Del. He left the service without commenting to reporters. Obama was attending church in Eau Claire.
McCain, who had no public schedule Sunday, told CBS News that Biden was a "wise selection" who will be formidable. But the Arizona senator was critical of the Obama-Biden ticket on foreign policy, citing disagreements with Biden's decision to vote against the first Gulf War as well as his position that Iraq should be divided "into three different countries."
McCain, who has not announced his running mate, holds a 2-1 lead over Obama as more knowledgeable on world affairs and as better suited to be commander in chief, according to an ABC News-Washington Post poll released Sunday. The same poll, which gave Obama a slight 49 percent to 43 percent lead overall, found that three-fourths said the addition of Biden would make no difference in their vote, while the remainder were evenly split on whether it would make them more or less likely to vote for Obama.
Axelrod spoke on ABC's "This Week" while Kaine and Ritter appeared on "Fox News Sunday."