The longest, most expensive White House race in history still has eight months to run before the November elections and even the pundits are perplexed as how it will play out.
Upcoming votes in four states on Tuesday could decide the fates of the candidates on both the Republican and Democratic sides -- or leave everything still to play for certainly for the Democratic party hopefuls.
Here are some possible scenarios after Tuesday's votes in Texas, Ohio, Vermont and Rhode Island:
Arizona Senator John McCain is likely to emerge as the official candidate of the Republican Party to stand in November's presidential elections.
According to independent pollsters RealClearPolitics.com, McCain already has some 1,019 delegates, just 172 short of the 1,191 needed to win the party's nomination.
His rival ordained Baptist preacher Mike Huckabee has only 254. There are some 265 delegates up for grabs on Tuesday night, with McCain set for a clean sweep.
The picture is more confused on the Democratic side, with New York Senator Hillary Clinton and Illinios Senator Barack Obama locked in a fight for the party's nomination and running neck-and-neck in the biggest primaries, Texas and Ohio.
According to RealClearPolitics.com, Obama has some 1,377 delegates compared to 1,279 for Clinton of the 2,025 needed to become the party's presidential candidate.
A total of 370 delegates will be at stake on Tuesday, but the Democratic Party awards them proportionally, so even if Clinton or Obama won all four states on Tuesday they would still not cross the threshold.
If Obama wins Ohio and Texas, after 11 nominating victories in a row, it could give him unstoppable momentum going into the next primaries. But Clinton does not have to throw in the towel, even though she is likely to come under huge pressure to abandon her bid to be the country's first woman president.
If Clinton wins either Texas or Ohio, she would most likely carry on towards the Pennsylvania primaries on April 22.
If Clinton wins both, her faltering campaign is suddenly reignited and the party's 795 superdelegates, who can vote for anyone they choose, will play a decisive role in the party's August nominating convention in Denver, Colorado. (AFP)
US White House race: what could happen next