WHAT IS SUPER TUESDAY?

* Super Tuesday is when 14 states across the US hold Democratic and Republican party primary elections.

* The outcome will likely have a major influence on who will represent the Democrats in the November 3 presidential election.

* Democrats in American Samoa and others living outside the US also get to vote on Super Tuesday.

* The Republicans and Mr Trump have it easy. Mr Trump faces little competition and in some states is running unopposed.

* The Democrat candidates will not have it easy. Super Tuesday will be a political knife-fight for the Democrats as they compete in Alabama, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont, Virginia and American Samoa.

* Bernie Sanders is hoping to cement his front-runner status on Super Tuesday against top challengers Joe Biden, Pete Buttigieg, Elizabeth Warren, Amy Klobuchar, Michael Bloomberg and Tom Steyer.

* Sanders took the early lead and Buttigieg was a close second after strong performances in the February 3 Iowa caucuses, February 11 New Hampshire primary and February 22 Nevada caucuses.

* Heading in to Super Tuesday, former vice president and one-time favourite Biden is hoping to keep his sinking campaign alive with a win in Saturday's South Carolina primary.

THE FIGHT FOR DELEGATES

* Each state primary is worth a certain number of delegates, who are allotted to candidates based on the number of votes they receive in each primary.

* Democratic presidential candidates are competing to be the first to collect a majority of the almost 4000 delegates spread across America's 50 states, territories and Washington DC.

* Super Tuesday is crucial because about one-third of all delegates, 1357, are up for grabs and candidates who perform badly are expected to drop out.

* America's most populous state, California, has 495 delegates on the table, Texas 228 and smaller states Arkansas and Maine have 36 and 32 respectively.

THE BLOOMBERG FACTOR

* All eyes will be on Bloomberg's Super Tuesday performance.

* The billionaire media magnate and former New York City mayor chose the unconventional strategy of skipping Iowa, New Hampshire, Nevada and South Carolina and going all-in on Super Tuesday.

* Bloomberg, worth an estimated $US60 billion ($A91 billion), has spent almost $US500 million of his own cash on his campaign but stumbled when he was savaged by Warren and other candidates in last week's Democratic debate.

THE RACE SO FAR

Sanders leads the polls (28 per cent according to the national polling average) and has the most pledged delegates so far (45).

Joe Biden is second in the national poll (16 per cent), Bloomberg third (15 per cent) followed by Warren (13 per cent), Buttigieg (10 per cent), Klobuchar (7 per cent) and Steyer (2 per cent).

Buttigieg (25 delegates) is second to Sanders in the delegate count with Biden third (15), then Warren (8) and Klobuchar (7) with the two billionaires, Bloomberg and Steyer, yet to pick up a delegate.

Australian Associated Press