The fate of Hillary Clinton's US presidential bid rested with voters in Ohio and Texas tonight in her hard-fought Democratic duel with Barack Obama.
Democratic presidential candidate Sen. Barack Obama of Illinois and his wife Michelle greet supporters at a rally in Houston, Texas.
Voters have been heading to the polls in Vermont, Rhode Island, Ohio and Texas. Voting ends in Ohio at 7.30pm (12.30am Irish time) and all voting in Texas will be over by 9 pm (2am Irish time).
Ms Clinton, a New York senator battling to snap Mr Obama's string of 11 consecutive state-by-state victories, needs wins in both Ohio and Texas to rejuvenate her struggling campaign and ensure the race moves on to Pennsylvania on April 22nd.
Losses in even one of the states could set off a stampede of party support for Mr Obama, raise pressure on Ms Clinton to drop out and make it even tougher to cut Mr Obama's lead in pledged delegates who will choose the Democratic nominee to contest November's presidential election.
Polls show Ms Clinton and Mr Obama in tight races in both Ohio and Texas - the biggest prizes today.
"I think I know what's happening and I believe that we're going to do well tomorrow," Clinton, who would be the first female US president, told reporters in Ohio yesterday.
"Then we move on to Pennsylvania and the states still ahead," she said. "So I'm just getting warmed up."
Ms Clinton gained ground on Mr Obama, an Illinois senator who would be the first black president, to take a slim lead in Texas and pull even in Ohio, according to a Reuters/C-SPAN/Houston Chronicle poll released today.
She took a 47 per cent to 44 per cent lead on Mr Obama in Texas, reversing his 3-point edge on Monday. The lead was within the poll's margin of error of 3.4 percentage points.
The race in Ohio was deadlocked at 44 per cent in the polling by Zogby International, a slight gain for Ms Clinton from Mr Obama's 2-point edge yesterday.
Today's contests also could put Republican front-runner John McCain, an Arizona senator, close to clinching his party's nomination.
Mr McCain is favoured to beat his last major rival, former Arkansas Govenor Mike Huckabee, in all four states.
Ms Clinton and Mr Obama made last-minute appeals for votes in Ohio and Texas yesterday.
Ms Clinton rose before dawn to tour a car plant in Toledo, Ohio, and closed the day with a televised town hall meeting in Texas with time bought by her campaign.
She renewed her attacks on Mr Obama over the North American Free Trade Agreement, an unpopular treaty in Ohio, which has suffered losses of manufacturing jobs.
Both say the treaty with Canada and Mexico should be renegotiated, but the Clinton campaign has highlighted reports that an Mr Obama adviser assured the Canadian government his opposition was political rhetoric and not substantive.
Mr Obama said his adviser, Austan Goolsbee, had simply reiterated to Canadian officials his views on the treaty. Canadian officials backed his version of the story.