Sanders won an overwhelming victory in Nevada, coming far ahead of his rivals and cementing his place as the opposition party's frontrunner.
If Sanders is the nominee, some Democrats worry Trump will hammer him on his long-buried words in defence of governments in Nicaragua, Cuba and the USSR.
Bernie Sanders won the New Hampshire primary election, the second state to pick a Democratic party candidate.
By nearly 2-to-1, respondents put November prospects at the top of their wish list, according to early exit poll data.
The results of the Iowa Caucus were delayed, causing chaos on the first key night of the US democratic party primaries.
The speeches added to the disarray in Iowa late Monday amid major delays in the reporting of results of the state's first-in-the-nation caucuses.
About two-thirds of voters participating in the caucus said they would rather see the Democratic Party nominate a candidate who "can beat Donald Trump."