With Super Tuesday now over, a clear front-runner has emerged for the U.S. Republican nomination, but the two main Democratic hopefuls remain locked in combat.

Voters from more than 20 states either voted in primaries or participated in caucuses.

Among the Republicans, Arizona Sen. John McCain emerged on top, winning major states like California, New York, Illinois and his home state.

The successful Republican candidate will need the support of 1,191 delegates at the party's convention in late August. McCain is believed to have won more than 700.

Former Massachusetts governor Mitt Romney, after first vowing to stay in the race, dropped out on Thursday after crunching the numbers (he trailed McCain by about 400 delegates). That leaves former Arkansas governor Mike Huckabee (195 delegates) as the only serious challenger - and some suspect the writing is on the wall for him.

Huckabee, an ordained Baptist minister, had strong support among white, born-again Christians, according to Super Tuesday exit poll results. Romney did well with those who identified themselves as conservatives.

McCain, considered a maverick by many in his party, had strength among moderates and independents. Veterans, older voters, Hispanics and men tended to support him.

He was given high marks for being the best qualified to be commander-in-chief and to handle the economy.

Unless something unexpected happens, McCain appears to be on track to become his party's nominee. Still, problems remain for him.

Dan McGroarty, a former speechwriter turned political consultant, told Canada AM on Wednesday that the winner-take-all nature of many of the Republican contests overestimated McCain's true strength, as many of his state victories were quite narrow in margin.

Allan J. Lichtman, a presidential historian at American University, said although McCain has won the nomination, he hasn't yet won the love of conservatives.

"That was clearly indicated by Huckabee's surprising strength in the South ... and Romney's strength in the West. John McCain has a lot of work to do to knit this party together," Lichtman Canada AM on Wednesday.

Powerful conservative voices like talk radio host Rush Limbaugh and James Dobson of Focus on the Family "have been vitriolic in their denunciations of McCain," Lichtman said.

Stephen Farnsworth of the University of Mary Washington told CTV Newsnet that conservatives might become resigned to McCain because he would be the strongest candidate in the actual presidential election with swing voters.

University of Toronto political scientist Renan Levine told CTV.ca that a bigger problem for McCain will be energizing the Republican base, which is something President George W. Bush did well, especially in 2004.

More than 62 million people voted for Bush in 2004 - an increase of 12 million over his 2000 total and almost 23 million more than who supported Republican nominee Bob Dole in 1996.

"I think the big riddle for a lot of people is, will this Republican base be inspired to go vote to stop someone like Hillary Clinton or even (Barack) Obama?" he said. "People tend to be inspired more to vote more often by a candidate they like, as opposed to, 'I am voting to stop the candidate I dislike'."

However, McCain hasn't come this far by being a bad politician, Levine said.

The Democrats

For the Democrats, more bruising political battles lie ahead, possibly into early summer and beyond.

Neither Sen. Hillary Clinton of New York, hoping to become the U.S.'s first female president, nor Sen. Barack Obama of Illinois, hoping to become the first black one, claimed victory Tuesday night.

The Democratic Party uses a complex system of proportional allocation of delegates, so merely winning a state doesn't mean a candidate takes all its delegates.

Obama won the most states -- 13. However, Clinton won eight, including ones with the most delegates, such as New York and California (she has a tiny edge in New Mexico, with all the votes not yet counted). An official delegate count isn't yet available, but the winning candidate will need the support of 2,025 delegates at the convention in late August.

Even though Sens. John Kerry and Ted Kennedy had endorsed Obama, Clinton took Massachusetts.

"It just shows how little endorsements count for in American politics," Lichtman said.

"It shows a lot of working-class people in Massachusetts thought Hillary Clinton had a better plan for their future than Barack Obama."

In the southern state of Georgia, eight of 10 African-Americans supported Obama, he said.

National exit polls show overwhelming support for Obama amongst blacks.

Exit polls in California show that Clinton had the support of about 70 per cent of Hispanics and three-quarters of Asian voters. Nationally, Clinton had the support of about two-thirds of Hispanics.

Those polls also showed the two were about even in support among white men, which is an improvement for Obama.

Clinton maintains an advantage with women voters. Young people have a crush on Obama.

The next steps

Lichtman said the battle among the Democratic heavyweights goes on -- and could continue for months.

"This is trench warfare," he declared. "Remember, the Democrats don't have winner-take-all primaries, so it's going to be very difficult to break this logjam."

Ultimately, the race could conceivably come down to who the approximately 800 "super delegates" -- elected politicians and party officials -- decide to support, he said.

There could also be a fight over whether to seat delegates from Michigan and Florida. Those delegates were disqualified when the states moved up their primaries without permission, Lichtman said.

"It's absolutely unpredictable, and both Obama and Clinton have their very enthusiastic supporters. Both have a very strong claim on being powerful candidates."

The next tests come in Louisiana and Nebraska on Saturday, and in Maryland, Virginia and the District of Columbia on Tuesday.

Those states have demographics that favour Obama. Clinton strategists prefer to talk about the March 4 primaries in Texas and Ohio, or the April 22 contest in Pennsylvania.

Obama's stunning momentum surge has given him the fundraising edge. He raised more than US$32 million in January, compared to about $13 million for Clinton, who loaned herself $5 million recently.

Levine said neither side has unlimited resources, and they will pick their battles in the coming primaries.

Whatever happens, Lichtman said this election could be historic, and not just because a black man or white woman could become president.

"This is a turning-point election. This is the end of the Bush era, and it could be the end of the conservative era that began with Ronald Reagan," he said.

Farnsworth said the "ballot question" for the Democrats increasingly appears to be about change, and if that's true, the advantage could shift to Obama.

With files from The Associated Press