WASHINGTON (MarketWatch) - Sens. Barack Obama and John McCain won the Democratic and Republican primaries in Vermont on Tuesday night, scoring early victories on a day that will see voters in four states weigh in on the race for the White House.

Voters went to the polls in Vermont, Texas, Ohio and Rhode Island against an increasingly grim backdrop of a slowing economy and growing financial uncertainty.

For Hillary Clinton, after losing the last 12 straight contests to Obama, the outcome of the races could determine whether she continues in the race to the White House or whether she decides to bow out.

On the Republican side, Sen. John McCain of Arizona was expected to sweep all four contests and gain enough delegates to garner him his party's nomination.

Officials in the delegate-rich and critical states of Ohio and Texas said they were expecting record turnouts, a sign of the intense competition between the two Democratic White House hopefuls.

Jobs and the economy were key issues among anxious voters, according to exit polls from MSNBC. Concerns about the impact of globalization on domestic jobs was a big issue, although to different degrees in the more hard-hit state of Ohio and the more prosperous Texas.

Among Ohio Democrats, 81% think international trade takes away jobs, compared to 72% who felt that way in 2004. Only 8% think it creates jobs, versus 13% in 2004.

In Texas, 59% of Democrats think international trade takes jobs, versus 62% in 2004. Twenty-four percent think it creates jobs.

High turnout

As many as 52% of Ohio's registered voters may turn out on Tuesday, CNN reported, citing Ohio's secretary of state. That would be 15 percentage points higher than in past presidential primaries.

The latest polls in these two delegate-rich states indicate that Clinton may have at least halted Obama's momentum, and perhaps turned things back her way, particularly in Texas -- the biggest prize in the four-state contest.

Texas and Ohio are on largely different economic pages. Between 1997 and 2007, Texas added 1.6 million jobs while Ohio shed 10,400. Texas's unemployment rate was 4.5% in December 2007; Ohio's was 6%. Per-capita income rose 55% in Texas between 1996 and 2006. In Ohio, it rose 43%.

Clinton's vow to fight on

On Monday, the former first lady suggested she'll fight on with her campaign regardless of what Tuesday's results bring, according to the Associated Press.

"I'm just getting warmed up," she told reporters in Toledo, Ohio.

The New York senator had a double-digit lead in Texas as little as three weeks ago, but Obama quickly whittled that away and some polls showed he had taken control. Now it appears the tide may have turned for Clinton.

She holds as much as a six-point lead, according to some recent surveys. An average of recent polls compiled by RealClearPolitics.com gives Clinton a 1.7% lead.

In Ohio, Clinton's lead seems more solid even though some polling showed Obama was catching up. The RealClearPolitics.com average shows her with a 7.1% lead. Some surveys showed that Obama had caught up to her in Ohio, a state that was expected to be firmly in her camp.

On the Republican side, Tuesday appears to be the day McCain will lock up the delegates he needs for the GOP nomination. McCain has 1,014 of the 1,191 delegates he needs to win the nomination. Tuesday's four winner-take-all Republican contests will yield 265 delegates.

Clinton badly needs to win big on Tuesday, having lost 11 straight contests to Obama. Back on Feb. 19, after losing Wisconsin's primary to Obama, she said Texas and Ohio would be the "firewall" where she could stop the first-term Illinois senator.

Trading promises

Clinton led Obama in early polls going into Ohio's contest, but he steadily closed the gap with her as election day in the hard-hit manufacturing state drew closer. In a debate in Ohio before Tuesday's vote, both Democratic candidates said they'd strive to make international trade agreements fair to U.S. workers.

Polls close in Ohio at 7:30 p.m. Eastern. Obama and Clinton are wrangling over 161 delegates in the Buckeye State, which has shed jobs due to the manufacturing downturn. Read more about the Ohio race.

In Texas, a total of 193 delegates are up for grabs, with 126 of those selected through the initial primary process. The remaining 67 delegates will be chosen through caucuses. Another 35 super-delegates are also part of the mix in the Lone Star State. Read a preview of the Texas contests.

Clinton and Obama have sung a different tune on trade in Texas, where the North American Free Trade Agreement, or NAFTA, is credited with helping border communities. Read more about the Democrats and trade.

All polls close in Texas at 9 p.m. Eastern, but caucuses will run for as long as two hours afterward.

Vermont and Rhode Island are also holding nominating contests on Tuesday. But with a combined 55 delegates at stake for the Democrats, the stakes don't stack up compared to Ohio and Texas.

Vermont's polls are the first to close on Tuesday, at 7 p.m. Eastern. Polls in Rhode Island close at 9 p.m. Turnout was expected to be about 30% in Rhode Island, media reports said.

Clinton appeared likely to win Rhode Island's 32 delegates, having enjoyed a comfortable lead in a Rasmussen poll there over Obama in late February. Vermont, with 23 delegates, is thought to be solidly in Obama's camp, though no surveys were available.