Mitt Romney notched early wins as he fought to establish his dominance in the race for the Republican U.S. presidential nomination on Tuesday but Ohio, the biggest prize of the evening, was too close to call.
Romney won as expected in Virginia, Vermont and his home state of Massachusetts, while rival Rick Santorum captured Oklahoma and Newt Gingrich won Georgia, according to network projections. Results from the five other states holding contests on "Super Tuesday," the biggest day so far in the roller coaster Republican campaign, were expected in the coming hours. More than 400 of the 1,144 delegates needed to win the party's nomination are at stake.
Polls in recent days showed Romney had effectively erased Santorum's lead in Ohio, a traditional bellwether state that could play an important role in deciding the Republican nominee to challenge Democratic President Barack Obama on November 6. Television networks said the race was too close to call after voting concluded at 7:30 p.m. EST (0030 GMT Wednesday).
Exit polls showed that Ohio voters viewed Romney as more likely to defeat Obama, but thought Santorum was more sympathetic to average Americans' concerns.
Tennessee was also too close to call. Contests were also being held in Idaho, Alaska and North Dakota.
A victory in Ohio and a good showing elsewhere would make Romney, a former Massachusetts governor, the favorite to win the nomination. Even without an Ohio win, his strength in other states all but ensures he will extend his lead in the delegate count.
"This is a process of gathering enough delegates to become the nominee, and I think we're on track to have that happen," Romney said after voting in his home town of Belmont, Massachusetts.
A less impressive showing could prompt renewed doubts about his ability to secure the nomination as Republicans continue the state-by-state battle to pick a nominee at their August convention.
Romney, who built a fortune of at least $200 million as a private-equity executive, has struggled to connect with conservatives and blue-collar voters in a campaign that has focused on his business career.
"He doesn't really know what he stands for," said Santorum supporter Katherine Frenz, 36, of Hilliard, Ohio.
In the last days of the Ohio campaign Romney made a point of trying to attract blue-collar voters, but CNN's exit poll indicated that Santorum received more support among those who said their annual income was $30,000 to $100,000, a group that made up 55 percent of the electorate there. Romney topped Santorum among voters with income of more than $100,000, while those who earned less than $30,000 were divided between the two candidates.
Santorum, a former U.S. senator from Pennsylvania, has won the support of religious conservatives thanks to his opposition to gay marriage and his views on other hot-button social issues. He has fought charges that his Senate career makes him a "Washington insider" and culture warrior who would alienate independent voters as Romney has pelted him with negative ads.
Gingrich, a former speaker of the House of Representatives, was counting on his Georgia win to claw his way back into contention. Ron Paul, a U.S. congressman from Texas known for his libertarian views, hopes to score his first win in Alaska.
In recent presidential campaigns, the Super Tuesday wave of primaries and caucuses has often settled the Republican race. But while this year's contests could establish a clear pecking order, the race is likely to stretch until April or May under new rules designed to attract more voters and boost enthusiasm.
But recent polls indicate the lengthy primary season may actually be alienating voters. An ABC News/Washington Post poll released on Tuesday showed that more voters view the candidates negatively than positively. An NBC News/Wall Street Journal poll on Monday found that 40 percent of voters view the Republican Party less favorably than they did before voting started in January.