Barack Obama is close to clinching the Democratic presidential nomination tonight, gaining support from a steady parade of uncommitted delegates and pushing rival Hillary Clinton to the verge of defeat.
A dozen superdelegates - party officials free to back any candidate at the August nominating convention -- announced their support for Obama, putting him within 30 delegates of the 2,118 he needs.
The Illinois senator, who would be the first black nominee of a major US political party, hopes to clinch the honor after polls close in the final two contests in Montana and South Dakota. Those states have 31 delegates at stake.
The Clinton campaign said she did not plan to concede to Obama at a New York rally later tonight.
"The nomination fight goes on until somebody gets the magic number and that isn't there today and that is not at all what Senator Clinton is going to talk about tonight," Clinton campaign chairman Terry McAuliffe told CNN.
Voting ends in South Dakota at 0100 Irish time and in Montana an hour later, with results expected shortly after.
More than 150 superdelegates remain undecided, and the conclusion of the voting could ignite a stampede toward Obama that would push him over the top.
But the Obama campaign has been urging superdelegates to make their endorsement before the voting ends, so the delegates he wins in the two states can allow him to clinch the Democratic race.
A group of 17 uncommitted Senate Democrats met to discuss the timing of a potential endorsement of Obama.
They will meet again tomorrow but are not expected to make their announcements by Tuesday night, a Senate aide said.
"I want all the primaries to play out before I make my final decision to endorse a Democratic Party presidential nominee," said Sen. Tom Carper of Delaware, one of the uncommitted senators.
"Senator Clinton needs to be left alone. Let's get through the primary process and let this week work it's course," Senate Democratic Leader Harry Reid told reporters.
A steady flow of superdelegates made their announcements throughout the day. Former President Jimmy Carter will endorse Obama when the polls close, the Carter Center said.
US Rep. James Clyburn of South Carolina, third-ranking Democrat in the US House of Representatives and the top-ranking black member of Congress, formally announced his support and urged other superdelegates to announce their decisions so Obama could wrap things up by day's end.
"Today the process ends," Clyburn told NBC's "Today" show.
Obama planned a victory celebration to kick off the general election campaign against McCain after the South Dakota and Montana polls close. He will hold it at the St. Paul, Minnesota hockey arena that will host the Republican convention in September.
Clinton and her campaign have sent mixed signals over the last two days about how long she would stay in a presidential race that she began as a heavy favorite but now has little chance of winning.
Campaigning in South Dakota, she said the end of the voting marked "the beginning of a new phase of the campaign" in which she will seek to convince superdelegates that she would be the strongest candidate against McCain in November.
With no more campaign trips to plan, workers who handle Clinton's advance travel arrangements have been told to go to New York or head home until further notice, aides said.
Both Obama and Clinton will speak to a pro-Israel lobbying group in Washington on Wednesday, and Obama said he expected to be talking to Clinton again soon.
He said he told her in a phone conversation on Sunday that "once the dust settled I was looking forward to meeting with her at a time and place of her choosing."