WASHINGTON – The biggest day yet in the US presidential campaign and most anticipated of the primary season has come, as the major candidates scurry throughout the country to build on leads or overcome deficits in the contests that could largely shape the outcome of the race.

Nearly half of the US states will hold votes on "Super Tuesday" to put their stamp on which Democrat or Republican should represent their party in the 4 November presidential election. Twenty four states will hold caucuses or primaries on a day many political junkies regard as a national referendum on the candidates.

The race has narrowed since the contest in Florida January 29. Former New York mayor and onetime Republican frontrunner Rudy Giuliani exited the race Wednesday after a weak third place showing in the state he had relied on to propel back into the front of the pack.

John Edwards, who was mostly stuck in third place finishes in the first six states, also jumped out of the campaign Wednesday, shrinking the Democratic field to heavyweights Hillary Clinton and Barack Obama.

Never in the history of the party nomination process have so many states held votes simultaneously. Over the last several presidential elections, the states have inched up their dates to have a greater say in the ultimate outcome.

Super Tuesday could make or break a candidate and requires big bucks and an endless amount of energy to campaign effectively in states spread across the nation, including delegate rich California and New York, two states on opposite coasts of the country.

The candidate with perhaps the most to gain on Super Tuesday could be John McCain, the senator from Arizona and Vietnam War veteran who solidified his frontrunner status with his victory in Florida.

A sweep could boost McCain to an insurmountable lead over the next strongest candidate, Mitt Romney, in the delegate count and get him close to the 1,191 delegates a Republican needs to capture the nomination. There are 1,018 delegates up for grabs on Tuesday, and McCain already has 93 to Romney’s 59 delegates.

On the Democratic side, Clinton and Obama are neck-and-neck and it’s unlikely either one will be forced out of the race based on Tuesday’s results. The Clinton and Obama camps have grown increasingly hostile in exchanging barbs over the role of race relations in the campaign for the Democratic nomination.

Clinton – along with husband and former president Bill – has always been popular among black voters and was relying on their support to become the first woman to win the White House. But Obama, who would be the first black president, has peeled away that support.

Obama soundly defeated Clinton in the South Carolina primary on Saturday, mostly because he overwhelmingly won the black vote in the southern state with a large African American population.

Clinton remains ahead of Obama in national media polls, but Obama’s campaign has been successful in targeting many of the smaller states whose tallies could add up and keep him in the race, even if the former first lady wins most of the big states.

Democrats need 2,025 delegates to secure the nomination and 2,084 are in play on Tuesday. Clinton is leading with 256 delegates compared to Obama’s 181. The wild card could still be held by Edwards, who had 64 delegates before bowing out but could give a bump to either of the candidates by offering his endorsement.

A poor showing on Tuesday could end the campaign of lower tier Republican candidates Mike Huckabee, the former governor of Arkansas, and Congressman Ron Paul, who has not been a factor in the race.

Huckabee surprised the Republican field by winning the first contest in Iowa on 3 January, but was unable to keep the momentum and has since not won a state.

[Copyright dpa 2008]

Subject: Super Tuesday, US elections, primaries