(CBS/AP) The polls have closed in South Dakota and CBS News estimates Barack Obama has secured the support of enough delegates to the Democratic National Convention to lay claim to the mantle of presumptive nominee.
Earlier in the day, a senior Hillary Clinton, campaign official confirmed to confirmed to CBS News that if Obama secured the necessary delegates to be the nominee, Clinton would "acknowledge but not concede" the race tonight. The official says "she has no plans to concede the race tonight."
A top Clinton adviser told CBS News chief White House correspondent Jim Axelrod that when Clinton decides to get out of race, she'll call her supporters directly to try to ensure that they fall in line behind Obama.
Obama received a steady stream of superdelegates since this morning as he approached the magic number of 2,118. This includes several Michigan superdelegates who endorsed him today and are only awarded one half vote each.
The Clinton campaign released a statement today saying "Senator Clinton will not concede the nomination this evening." Campaign Chairman Terry McAuliffe told CNN this morning that Obama "doesn't have the numbers today, and until someone has the numbers the race goes on."
Polls close in Montana at 10 p.m. EDT.
According to CBS News exit polls, most South Dakota Democratic voters (55 percent) think the length of the primary campaign has energized the party, while 39 percent say it has divided it. Fifty-five percent say that Obama should pick Clinton as his vice president, if he is the nominee.
Less than half (45 percent) of Clinton voters in South Dakota and Montana say they would be satisfied with Obama as the Democratic Party's nominee, while 53 percent in South Dakota and 52 percent in Montana would be dissatisfied. Most Obama voters (54 percent) in South Dakota would be satisfied with Clinton as the nominee, while 45 percent would not. But in Montana, only 48 percent of Obama voters would be satisfied with Clinton as the nominee.
Sixty-one percent of South Dakota Clinton voters and 60 percent in Montana say they would vote for Obama in a general election, while 16 percent in South Dakota and 25 percent in Montana would vote for McCain. If Clinton were the nominee, 73 percent of South Dakota Obama voters and 65 percent of Montana Obama voters would back her, while 13 percent of Obama backers in South Dakota and 20 percent in Montana say they would support McCain.
Most Democrats in both states (60 percent in South Dakota and 67 percent in Montana) say that Obama's decision to leave Trinity Church was not important in their vote, while 37 percent in South Dakota and 28 percent in Montana say it was important.
More superdelegates endorsed Obama Tuesday morning, bringing him closer to becoming the nation's first black presidential nominee from a major party. Nearly 200 superdelegates have yet to make an endorsement. They were expected to rally behind Obama in short order.
One of those superdelegates yet to formally endorse was Former President Carter, who told the Associated Press he'd endorse Obama after the polls close on the final primaries. "The fact is the Obama people already know they have my vote when the polls close tonight," Mr. Carter said.
Clinton, once seen as a sure bet in her historic quest to become the first female president, was still pressing the superdelegates to support her fading candidacy. But McAuliffe indicated she was not inclined to drag out a dispute over delegates from the unsanctioned Michigan primary despite feeling shortchanged by a weekend compromise by the party's rules committee that she could still appeal to a higher level.
"I don't think she's going to go to the credentials committee," he said on NBC's "Today" show. Taking the matter to that committee would essentially extend the dispute into the convention and deny Democrats the unity they sorely want to achieve against Republican John McCain.
Seeing the cards fall into place for his November rival, McCain planned a prime time speech Tuesday night in the New Orleans suburb of Kenner, La., in what is essentially a kickoff of the fall campaign.
Obama told The AP on Monday that "we've got a lot of work to do in terms of bringing the party together" with the convention approaching.
"Once the last votes are cast, then it's in everybody's interest to resolve this quickly so we can pivot," he said.
In a defiant shot across the GOP bow, Obama, who returned to hometown Chicago late Monday, planned to hold his wrap-up rally in St. Paul, Minn., at the arena that will be the site of the Republican National Convention in September.
In his remarks in St. Paul, Obama will be gracious toward his Democratic rival, repeating the praise he's lavished upon Clinton in recent days, reports CBS News correspondent Dean Reynolds, while calling for much needed party unity to take the battle to the Republicans in November.
Clinton returned to New York, the state she represents in the Senate, planning an end-of-primary evening rally in Manhattan after a grueling campaign finale as she pushed through South Dakota on Monday.
"I'm just very grateful we kept this campaign going until South Dakota would have the last word," she said at a restaurant in Rapid City in one of her final campaign stops.
The Associated Press also reports Clinton has told congressional colleagues she would be open to becoming Obama's vice presidential nominee, saying she would consider it if it would help Democrats win the White House.
Clinton made the comment on a conference call with other New York lawmakers Tuesday, according a participant on the call.
The senator's remarks came in response to a question from Democratic Rep. Nydia Velazquez who said she believed the best way for Obama to win over key voting blocs, including Hispanics, would be for him to choose Clinton as his running mate.
"I am open to it," Clinton replied, if it would help the party's prospects in November.
Clinton still sounded buoyant. Her biggest booster and most tireless campaigner, husband Bill Clinton, didn't. "This may be the last day I'm ever involved in a campaign of this kind," the former president said somberly as he stumped for her in South Dakota.
Ahead of Tuesday's concluding primaries, Obama sought to set the stage for reconciliation, praising Clinton's endurance and determination and offering to meet with her - on her terms - "once the dust settles" from their race.
"The sooner we can bring the party together, the sooner we can start focusing on McCain in November," Obama told reporters in Michigan. He said he spoke with Clinton on Sunday when he called to congratulate her on winning the Puerto Rico primary, most likely her last hurrah.
That fueled speculation for a "dream ticket" in which Clinton would become Obama's running mate - but neither camp was suggesting that was much of a possibility.
In the AP interview, Obama was asked when he would start looking for a running mate.
"The day after I have gotten that last delegate needed to officially claim the nomination, I'll start thinking about vice presidential nominees," he said. "It's a very important decision, and it's one where I'm going to have to take some time."
©MMVIII, CBS Interactive Inc. All Rights Reserved.