The destiny of the searing Democratic White House battle is on the line in two key states Tuesday, with Barack Obama seeking a knockout, and Hillary Clinton desperately reaching for a lifeline.
Bold, brash Texas, and economically distressed Ohio have the chance to deal a decisive blow in the increasingly angry race, in which one hopeful will make history, as the first black, or woman presidential nominee.
Obama, 46, hopes to take his winning streak to 15 straight nominating contests, on a day which also includes voting in Rhode Island and Vermont.
Clinton, 60, needs to come out of Tuesday with a reason to go on, as she currently trails Obama in nominating delegates, fundraising, the popular vote and momentum, in the race to battle likely Republican nominee John McCain.
Senator McCain, the Vietnam war hero who has pulled off a stunning comeback after his campaign was left for dead last year, hopes to finally nail down the Republican nomination, by dispatching pesky challenger Mike Huckabee.
He is tipped to pick up the remaining support he needs to cross the threshold of 1,191 delegates to the party convention in September.
Should Clinton lose both Ohio and Texas, she would face intense pressure to fold her White House campaign for the good of the party.
"We have to win on Tuesday, that's not a surprise to any of you and we are going to win on Tuesday," the former first lady said in Texas on Saturday.
But the campaign may be regretting the categorical marker laid down by former president Bill Clinton last month.
"If she wins in Texas and Ohio, I think she'll be the nominee," Bill Clinton told supporters in Beaumont, Texas. "If you don't deliver for her, I don't think she can be. It's all on you."
In recent days, the Clinton campaign has appeared to be scratching around for a reason to stay in the contest, should she fail to pull off a double win, with recent polls giving Obama a lead in the Lone Star state.
"If (Obama) is unable to win all four states, it shows that Democrats are engaged in what some in the media have referred to as buyer's remorse, that there is an interest in having this campaign go on and go on into at least Pennsylvania and beyond," Clinton spokesman Howard Wolfson said last week.
But the Obama campaign has dismissd as "lunacy" Clinton's argument that the race for the nominating delegates, who will anoint the nominee is still close.
They say the Illinois senator is more than 150 ahead, and say 'superdelegates' the 795 party luminaries who can vote how they like at the party convention, are streaming to Obama's side.
The upshot, according to the Obama camp, is that Clinton needs landslide wins in Ohio and Texas, Pennsylvania, which votes April 22, and beyond, just to catch up.
Such a scenario seems unlikely, as latest polls in Texas and Ohio have the race a virtual dead-heat, but with some signs Obama is cutting into Clinton's core vote of white blue collar voters and Hispanics.
A new Reuters/C-Span-Zogby survey found Obama leading Clinton 45 per cent to 43 per cent in Texas. A previous poll by Zogby released Friday had Obama up 48 to 42 per cent.
In Ohio, the rivals were tied at 45 per cent, according to Saturday's poll.
As the March 4 contests loomed, Clinton, breathing defiance as pundits wrote her off, launched a string of fierce attacks on Obama's capacity to serve as commander in chief.
Obama hammered back hard, mocking Clinton's vows to forge change, saying her vote for war in Iraq, was just a sign of a shifty style of politics.
But a day after implying in a campaign ad her Democratic foe was unfit to answer an urgent 3:00 am foreign policy crisis, the New York senator said Obama's whole campaign was based on one anti-Iraq war speech in 2002.
Obama's spokesman Bill Burton was equally as scathing in response.
"On one of the only major foreign policy decisions she has ever faced in her career, Senator Clinton chose to follow the politics of the moment instead of the conclusions in the National Intelligence Estimate and voted for a war that has made us less safe and less secure," he said referring to Clinton's 2002 vote to authorise the use of force in Iraq, a war Obama opposed. (AFP)
Day of destiny looms in White House race