By Sara Puig, with Michael Mathes in Washington
Democratic presidential frontrunner Hillary Clinton will finally square off with top rival Bernie Sanders in the party's first debate of the 2016 campaign as she seeks to prove she is the candidate to beat.
Clinton on Tuesday will take centre stage in Las Vegas with Sanders, an independent senator from Vermont who has drawn huge crowds on the campaign trail, and three other hopefuls seeking to make their mark with a national audience.
The debate starts in Sin City at about 6pm local time (1300 NZT).
The spotlight therefore is likely to be on Clinton and Sanders.
While there is unlikely to be a dramatic clash of personalities as seen in the first two Republican debates, the former secretary of state will no doubt face pressure from the upstart senator in their much-anticipated encounter.
The other three challengers - former Maryland governor Martin O'Malley, ex-senator Jim Webb and former Rhode Island governor Lincoln Chafee - will try to generate breakout moments to show they are electable alternatives to Clinton.
The 67-year-old Clinton is nearly eight years removed from her campaign clashes with ultimate White House winner Barack Obama, and part of her goal will be to show she still has expert debate skills even though she appears to struggle to personally connect with voters.
Besides focusing on her proposals for gun control, Wall Street regulations and other policies, Clinton will want to prove that she can be the first woman to win the White House, despite a recent downward trend in her poll numbers.
Clinton still leads nationally in polls, but she trails Sanders by nearly 10 points in New Hampshire and holds only a modest lead in Iowa, both key early-voting states.