Voting is underway across Nevada as the most diverse state so far has its say in the Democrats' nomination fight.
Uniformed housekeepers and casino workers streamed into the Bellagio on Saturday, one of seven casino-resorts on the Las Vegas Strip among 200 caucus locations statewide hosting caucuses.
Nevada is the third contest on a 2020 election calendar marked by chaos and uncertainty after the opening votes in Iowa and New Hampshire, overwhelmingly white, rural states.
The first presidential contest in the West will test the candidates' strength with black and Latino voters for the first time in 2020.
Nevada represents an opportunity for these candidates to demonstrate their appeal to a larger swath of our country, said state Attorney General Aaron Ford, a Democrat who is not endorsing a candidate.
Nevada's population aligns more with the U.S. as a whole, compared with Iowa and New Hampshire: 29 per cent Latino, 10 per cent black and 9 per cent Asian American and Pacific Islander.
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Minnesota Sen. Amy Klobuchar, a moderate who has struggled with minority voters, was already playing down the caucuses and looking past Nevada.
This is a big day. We're excited. But it is the beginning of the next chapter in our campaign, and this chapter is going to be really fast-moving because we have so many states that we're going to be covering, and so many events," she told volunteers at her Las Vegas campaign headquarters.
The vote comes at a critical moment for the Democratic Party.
Self-described democratic socialist Bernie Sanders has emerged as the clear front-runner as a half-dozen more moderate candidates savage one another.
Each wants to be the preferred alternative to the Vermont senator in the race to take on President Donald Trump in November.
Meantime, questions lingered about Nevada Democrats' ability to report election results quickly and new concerns surfaced about foreign interference in the 2020 contest.
Sanders confirmed reports that he had been briefed by US officials about a month ago that Russia was trying to help his campaign as part of Moscow's efforts to interfere in the election.
"It was not clear what role they were going to play," Sanders said.
"We were told that Russia, maybe other countries, are going to get involved in this campaign."
He added: "Here's the message to Russia: Stay out of American elections."