Bernie Sanders faces a test of his front-runner status in the Democratic White House race on Saturday in Nevada, where voters will consider an unsettled field of candidates as they search for a challenger to take on President Donald Trump.
Sanders, a self-identified democratic socialist senator from Vermont, has surged to the top of opinion polls nationally and in Nevada after strong performances in the first two nominating contests in Iowa and New Hampshire earlier this month.
While Sanders' rivals will try to blunt his momentum in Nevada, they each face significant challenges of their own.
Former Vice President Joe Biden and Senator Elizabeth Warren are looking to jump-start struggling campaigns after poor finishes in the first two states, while former South Bend, Indiana mayor Pete Buttigieg and Senator Amy Klobuchar are hoping to prove they can appeal to Nevada's more diverse electorate.
Voters will pour into more than 250 sites around Nevada to take part in the caucuses, and officials say they have taken steps to avoid the chaos that a malfunctioning app caused in Iowa by switching to a system with multiple backups using paper, phones and iPads.
Four days of early voting in Nevada this week drew more than 75,000 Democrats, more than half first-time voters, putting the party in position to surpass the turnout record of 118,000 in 2008, when Barack Obama's candidacy electrified the party.
The Nevada contest comes one day after the news broke that Sanders had been briefed by US officials that the Russian government was trying to help his campaign as part of an effort to interfere with the Democratic nominating contest.
"The intelligence community is telling us they are interfering in this campaign, right now, in 2020. And what I say to Mr. Putin, if elected president, trust me you are not going to be interfering in American elections," Sanders told reporters in Bakersfield, California.
The caucuses also follow a frenetic Democratic debate in Nevada on Wednesday that featured a volley of scathing attacks on Michael Bloomberg, the billionaire former mayor of New York City, who has been rising in the polls on the back of a self-funded advertising blitz but is not even competing in Nevada.
The next primary will be Feb. 29 in South Carolina, followed three days later by the Super Tuesday contests in 14 states on March 3 that pick more than one-third of the pledged delegates who will help select a Democratic nominee.
Trump, who narrowly lost Nevada by two percentage points to Democrat Hillary Clinton in 2016, visited Las Vegas on the eve of the caucuses on Friday and predicted another round of Iowa-style chaos at the caucuses.
"They're going to tell you about healthcare, they're going to tell you about our military and the jet fighters and the missiles and rockets, but they can't count votes," Trump said of Democrats.
"With your help this November we're going to defeat the radical socialist Democrats and we are going to win Nevada in a big, beautiful landslide," he said.
Nevada is the first nominating state with a diverse population after contests in predominantly white Iowa and New Hampshire. More than four of every 10 voters in the Nevada Democratic caucuses in 2016 were non-white, according to entrance polls.
Sanders has led national polls among Hispanics, who represented about one-fifth of the Democratic electorate in the 2016 Nevada caucus. In Nevada, Sanders has led the last five opinion polls, taking a lead over moderates Biden and Buttigieg, as well as his progressive ally Warren.
Sanders lost Nevada to Clinton by five percentage points during his first presidential bid in 2016, but this time he faces a far more splintered field that includes three centrist candidates - Biden, Buttigieg and Klobuchar - all vying to win votes of the party's moderate wing.
Buttigieg and Klobuchar, a senator from Minnesota, lag in support among non-white voters, who are a core part of the Democratic electorate and typically a significant factor in primary battles.
Biden is counting on a robust showing next week in South Carolina, where he has enjoyed strong support among the state's sizable bloc of African-Americans, although Sanders has pulled even with him among black voters in some recent polls.