Clinton has yet to acknowledge Obama's victory in the bruising Democratic race and her aides - also dodging that conclusion - said on the morning talk shows that she would take a few days to decide what comes next for her. Obama spoke by phone with her Tuesday night and both sides predicted he and Clinton would sit down together before long.
"When the dust settles and it makes sense for her, he'll meet whenever she wants to," Gibbs said. "She's accumulated a lot of votes throughout this country. We want to make sure that we're appealing to her voters."
On the final night of the primary season, Clinton won South Dakota on Tuesday while Obama took Montana - and a slew of party superdelegates who declared their support to help him clinch the nomination. He did it, according to The Associated Press tally, based on primary elections, state Democratic caucuses and support from superdelegates. It took 2,118 delegates to clinch the nomination at the convention in Denver this summer, and Obama had 2,154 by the AP count.
Pennsylvania Gov. Ed Rendell, a dogged Clinton supporter, recognized the brutality of the arithmetic.
"I am the last of the Mohicans, but it is over," he said.
But after all of Obama's struggles to win over white blue-collar workers and older voters who flocked to Clinton, Rendell said he remained "a little wary" about the Illinois senator's prospects.
"Senator Obama is an exciting candidate, he's smart as a whip, he's got the backbone," he said on CNN, "but he's got some work to do, no question about it."
Obama and Clinton were both back in Washington on Wednesday to address the national conference of the American Israel Public Affairs Committee.
The Rev. Jesse Jackson, who ran twice for the Democratic nomination in the 1980s and made what was then historic progress for a black candidate, praised Obama's achievement in a phone interview from Serengeti National Park in northeastern Tanzania, where he is attending a meeting.
"Obama's nomination reflects phenomenal growth in America," he told The Associated Press. "The dream of a promised land is being fulfilled."
He said Clinton "should accept the defeat graciously" and the two longtime rivals should strive for a quick reconciliation so that the party is united in the fall.
Four Democratic leaders, also eager for unity, said in a joint statement Wednesday that "the voters have spoken" and the remaining uncommitted superdelegates should declare their support for a candidate by Friday. They were Senate Majority Leader Harry Reid, House Speaker Nancy Pelosi, Democratic chairman Howard Dean and West Virginia Gov. Joe Manchin, head of the Democratic Governors Association.
Former Vice President Walter Mondale, a superdelegate who had been a Clinton support and the 1984 Democratic presidential nominee, endorsed Obama on Wednesday.
The primaries behind them, Obama and McCain were drawing the battle line for a fall fight that will make history with the election of either the oldest first-term president in McCain or the first black commander in chief in Obama. In speeches marking the start of the general election, both maneuvered for the advantage with voters sour on the status quo. Both were competing beyond their party's base, too.
"The key to winning the election is independent voters and Democrats as well," McCain said in an interview shown Wednesday on ABC's "Good Morning America." Even so, he said "I don't think so" when asked on CBS whether he'd pick a Democrat as his running mate.
Obama's racial groundbreaking was noted everywhere from the White House to the house of his Kenyan relatives from his father's side of the family.
"I've just watched him on television, and as a family we are very happy," his uncle, Said Obama, told AP from Kisumu in western Kenya. "Really, it is something that is a trendsetter."
White House press secretary Dana Perino said on behalf of President Bush: "Senator Obama came a long way in becoming his party's nominee. And his historic achievement reflects the fact that our country has come along way, too."
In St. Paul, Minn., Obama, 46, ceded no ground on the reformer mantle and cast McCain as a continuation of the unpopular Bush's eight-year tenure.
"My differences with him are not personal; they are with the policies he has proposed in this campaign," he said Tuesday. "Because while John McCain can legitimately tout moments of independence from his party in the past, such independence has not been the hallmark of his presidential campaign."
The campaign is the first in half a century in which neither a sitting president nor a vice president is running for the highest office, and the first since 1960 in which a senator will assume the White House. A fragile economy and an ongoing Iraq war, as well as matters of age and race, serve as a backdrop.