Moment of truth in US poll race

The Democrats face a duel, the Republicans a possible coronation. On Super Tuesday Mitt Romney enters the Last Chance Hotel.

Senator John McCain and Romney are not the only two candidates seeking the Republican nomination but they are the only two with a realistic chance of winning their party's backing to run for the presidency. ''America's Mayor'' Rudy Giuliani has endorsed McCain after he left the field following a catastrophic campaign.

For the Democrats it is a clear choice on Tuesday following the departure of John Edwards. This day alone will determine the allegiance of more than 1,600 of the 2,025 delegates needed to capture the nomination at the Democratic convention in Denver in August.

However Tuesday's 22 Democratic races will be settled by proportional representation, lessening the impact of winning delegate-rich states like California and New York. This almost guarantees that Barack Obama and Hillary Clinton will continue to slug it out possibly up to the convention.

It is a different scenario for the Republicans where McCain could possibly wake up on Wednesday morning as the de facto candidate giving him a massive advantage in preparing for the election.