Hillary Clinton refused to count herself out of the U.S. presidential race on Tuesday as her hard-fought duel with Barack Obama for the Democratic nomination rested with voters in Ohio and Texas.
Turnout was expected to be strong in states -- Ohio, Texas, Vermont and Rhode Island -- voting on Tuesday. Polls close in Ohio at 7:30 p.m. EST and all voting in Texas will be over by 9 p.m. New York time.
The first results could be available immediately after the polls close, although a very tight race could take hours.
Clinton, a New York senator battling to snap Obama's string of 11 state-by-state victories, needs wins in both Ohio and Texas to rejuvenate her campaign and justify keeping the
Democratic race alive until the next delegate-rich prize -- Pennsylvania -- votes on April 22.
Losses in even one of Tuesday's states could set off a stampede of party support for Obama, raise pressure on Clinton to drop out and make it even tougher to cut Obama's lead in the
pledged delegates who will choose the Democratic nominee to contest November's presidential election.
Tuesday's contests also could put Arizona Sen. John McCain, the Republican front-runner, close to clinching his party's nomination. McCain is favored to beat his last major rival,
former Arkansas Gov. Mike Huckabee, in all four states.
"I believe that with your help today that we can secure enough delegates to make sure that we can secure the nomination, but we have to win and we have to win big here in the state of Texas," McCain told supporters in San Antonio.
Opinion polls show Clinton and Obama in tight races in both Ohio and Texas -- the biggest prizes on Tuesday.
The former first lady, who would be the first female U.S. president, refused to mull how she would respond to a loss.
"I don't think like that. We're working hard," Clinton told reporters after greeting voters at a school. "We think we're going to do really well here in Texas and in Ohio."
Clinton had a slim lead in Texas over Obama, an Illinois senator who would be the first black president, and pulled even in Ohio, according to a Reuters/C-SPAN/Houston Chronicle poll
released on Tuesday.
She took a 47 percent to 44 percent lead on Obama in Texas, reversing his 3-point edge in the poll on Monday. The lead was within the poll's margin of error of 3.4 percentage points.
The Ohio race was deadlocked at 44 percent in the polling by Zogby International, a slight gain for Clinton from Obama's 2-point edge on Monday.
Obama stopped by a rodeo in Houston to check out some tractors and livestock and shake hands with potential voters. He made few comments except to say "I feel good."
Clinton's campaign aides have been tamping down expectations, easing away from talk that she needed to win both Ohio and Texas, with their combined 334 delegates at stake.
Obama noted the high stakes in a rally on Monday night.
"So here we are with the possibility of winning the nomination," Obama said in Houston. "One of the things that I've learned is that what makes this powerful is not that things always go easy, but rather that we are willing to go forward when it's hard."
Like her husband, former President Bill Clinton, who nicknamed himself "The Comeback Kid" for his improbable rise to the White House in 1992, Clinton has dodged disaster before.
In January, Obama appeared ready to deal her a knockout blow in New Hampshire after his big win in Iowa, but she defied opinion polls and won the victory.
After a landslide loss in South Carolina, Clinton battled Obama to a draw in Super Tuesday contests around the country on Feb. 5, winning some of the biggest prizes of the night in
California, New York and New Jersey.
Under Democratic rules allowing the losers in each state to win a proportional amount of delegates, Clinton cannot close the gap on Obama among pledged delegates unless she scores big wins in Ohio and Texas that appear beyond her grasp.
An MSNBC count gave Obama 1,194 delegates to Clinton's 1,037 before Tuesday's showdowns, well short of the 2,025 needed to win the nomination.