Barack Obama stepped to the brink of victory in the Democratic presidential race today, defeating Hillary Clinton in the Oregon primary and moving within 100 delegates of the total needed to claim the prize at the party convention this summer.

However, the night's results were again a mixed bag with his opponent Hillary Clinton winning Kentucky by a wide margin.

"It's clear that tonight we have reached a major milestone on this journey," Mr Obama said in an email sent to supporters even as the polls were closing in Oregon on the West Coast. "We have won an absolute majority of all the delegates chosen by the people in this Democratic primary process."

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With only three more contests to go, time is running out for Mrs Clinton. While her victory in Kentucky was overwhelming - beating Mr Obama by a margin of 65 per cent to 30 per cent - she still hasn't pulled off an upset win that might have attracted remaining uncommitted superdelegates to her side. Indeed in recent weeks and days, the flow of superdelegates has been lopsided in Mr Obama's favour.

Today, Mr Obama will underline at an arena rally in Tampa, Florida, his achievement in amassing a majority of so-called pledged delegates, those who are apportioned according to results through the whole caucus and primary process. It will be his first visit to Florida, which, like Michigan, has been disqualified from affecting the nomination race because it broke party rules by voting too early.

Mrs Clinton, by contrast, will use her huge Kentucky win to make the case that she can stay in the race until the last contests on 3 June in Montana and South Dakota. Speculation is mounting that she is positioning herself effectively to force Mr Obama to give her the vice presidential spot on his ticket.

Certainly there is almost no scenario left for her to win the nomination. Mr Obama needed only to pick up seventeen new delegates last night to secure a majority of pledged delegates. He didn't quite get them in Kentucky, but Oregon quickly put him over the top. He still needs the help of superdelegates, but he is clearly within striking distance of passing the magic mark of 2,026 formally to clinch the crown.

Mr Obama celebrated with supporters last night in Iowa, where he scored his first big win back in January. "We have returned to Iowa with a majority of delegates elected by the American people," he told a cheering crowd in front of the State Capitol in Des Moines, "and you have put us within reach of the Democratic nomination for president of the United States of America."

Mrs Clinton took the microphone in Kentucky as the sheer size of her win there became apparent. Her message was directed as much at uncommitted superdelegates as at the people in the room. "The stakes are high," she said. "After all this country has been through over the past seven years, we have to get this right. We have to select a nominee who is best positioned to win in November."

The former first lady is also counting on a meeting of the party's rules committee at the next weekend to reconsider the punishment dealt to Florida and Michigan. While some kind of compromise is likely to lengthen that goal-post number of 2,026, it may do little to help her in the long run.

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Indeed, despite crushing her opponent in Kentucky and last week in West Virginia, Mrs Clinton finds herself derided by sections of the media as "delusional", politely spoken of in the past tense by her rival and completely ignored by the Republican candidate, John McCain.

With the writing on the wall for Mrs Clinton's presidential hopes, she has been complaining about the "sexist" treatment she has endured from the pundits, the media and from others throughout the long and gruelling campaign.

"It's been deeply offensive to millions of women," Mrs Clinton told The Washington Post. "I believe this campaign has been a groundbreaker in a lot of ways. But it certainly has been challenging given some of the attitudes in the press, and I regret that, because I think it's been really not worthy of the seriousness of the campaign and the historical nature of the two candidacies we have here."

Mrs Clinton continues to make the case that she has the best chance of winning the presidency in November. Speaking at the high school here in the actor George Clooney's Kentucky birthplace, she shouted to her supporters that "this race is far from over!...I'm going to make my case and I'm going to make it until there's a nominee, and we're not going to have one today and we're not going to have one tomorrow and we're not going to have one the next day."

Even if the Kentucky and Oregon results deliver Mr Obama one unassailable measure of popular support: the majority of the delegates from the primaries and caucuses, he does not want to be attacked for pushing Mrs Clinton out of the race and has ordered his staff not to use the opportunity to proclaim victory.

Yet his camp will be hoping today that scoring that majority of elected delegates should create a flood of superdelegates – select Democratic Party officials – to Mr Obama's side and in effect hand him the nomination.

But to win the presidency he also needs the backing of Mrs Clinton's supporters, especially the white working-class voters who abruptly turned against him when the controversy erupted over his pastor Jeremiah Wright, whose criticisms of America jarred with the flag-waving patriotism of many voters.

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