WASHINGTON - Super Tuesday - March 3 - is the biggest day in the Democratic primary election calendar, when 14 states and one US territory will vote for the Democratic presidential nominee - the person who will eventually run against President Donald Trump in November.
To become the Democratic presidential nominee, candidates have to win a majority - at least 1,991 - of the 3,979 pledged delegates.
One third of these delegates will be available on Super Tuesday, far dwarfing the 4 per cent of delegates who were up for grabs in the early races in February.
Super Tuesday may produce a presumptive nominee. The sheer number of candidates available on March 3 means that anyone who does very well could make it hard for rivals to catch up after that.
At the moment, Vermont senator Bernie Sanders is the front runner. Former vice-president Joe Biden lags slightly behind him but is poised to catch up following his South Carolina win, and is backed by his moderate rivals who dropped out over the weekend: Minnesota senator Amy Klobuchar and former South Bend mayor Pete Buttigieg.
Polls close between 7pm and 11pm EST on Tuesday (8am to noon on Wednesday in Singapore).
The voting states are Alabama, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Virginia, and Vermont, as well as American Samoa.
Here are five things to watch out for:
1. WHO WILL CALIFORNIA AND TEXAS CHOOSE?
Both states have a massive number of delegates. California has 415 while Texas has 228, which together makes up nearly half of the 1,357 delegates available on Tuesday.
The sheer number of delegates available in these two states could easily upend the current field, possibly dethroning Mr Sanders or dashing Mr Biden's hopes for good.
California's results may not be known immediately, however, as the state typically takes a long time to count its votes.
2. HOW WIDE IS THE GAP BETWEEN FIRST AND SECOND PLACE?
The distance between the leaders of the pack will give a better idea of how long candidates will continue to duke it out.
If there is a clear front runner after Super Tuesday, the party can coalesce around him or her and focus on campaigning against Mr Trump.
But if there isn't, candidates will likely continue to fight it out until the Democratic National Convention in July, as eventual nominee Hillary Clinton and Mr Sanders did in 2016.
"If three or more are bunched together in the delegate count, they will all probably stay in the race, increasing the odds of no one getting a first ballot nomination at the Democratic Convention in Milwaukee in July," wrote Brookings Institution governance studies senior fellow Elaine Kamarck wrote on the think-tank's website last Tuesday (Feb 25).
But if two candidates emerge in close proximity to each other, there will be plenty of pressure for the losers to get out and pick sides, she said.
"If one candidate opens up a sizable lead over all the others, he or she will be hard to stop."
3. WILL BLOOMBERG'S GAMBLE PAY OFF?
Billionaire and former New York City mayor Michael Bloomberg will appear on the ballot for the first time on Tuesday after skipping the four early races in February to focus on Super Tuesday.
The media mogul has spent an unprecedented fortune on ads, staff and events, and is currently in third place in national polls, but has been untested so far.
Super Tuesday will be the first test of how much voters will actually support him.
4. WILL ANYONE ELSE DROP OUT?
Under the Democratic Party's rules, candidates need to win at least 15 per cent of the vote in a state to pick up a proportionate number of the state's delegates. If they do not meet the threshold, they get no delegates from that state.
Massachusetts senator Elizabeth Warren will face pressure to drop out if she does not perform well. She failed to win any delegates since Iowa on Feb 3 and may not even win in her home state of Massachusetts, where she faces strong competition from Mr Sanders.
Mr Buttigieg, who had won 26 delegates to her eight, dropped out on Sunday, while Ms Klobuchar who had one fewer delegate, dropped out on Monday.
Representative Tulsi Gabbard of Hawaii is also still in the race, despite not having picked up any delegates so far.
5. WILL THERE BE DISINFORMATION ON SUPER TUESDAY?
US authorities warned voters to be on the lookout for disinformation, following the 2016 presidential election in which Russia was found to have interfered in a 'systematic and sweeping fashion'.
In a joint statement on Monday, several state departments and agencies said that while they continued to work to keep the elections free from foreign interference, voters had a part to play too.
"Americans must also remain aware that foreign actors continue to try to influence public sentiment and shape voter perceptions. They spread false information and propaganda about political processes and candidates on social media in hopes to cause confusion and create doubt in our system," said Departments of State, Defence, Homeland Security, as well as the Office of the Director of National Intelligence, the Federal Bureau of Investigation, the National Security Agencyand Cybersecurity and Infrastructure Security Agency.