Democratic White House hopefuls barnstormed Nevada Friday hunting for votes on the eve of the latest contest in the nomination race, as the state seeks to avoid the chaos that marred Iowa's caucuses.

The battle to see who challenges Republican President Donald Trump in November has entered an urgent phase, with eight candidates including late entrant Michael Bloomberg, the former mayor of New York, scrambling for advantage.

Senator Bernie Sanders is the clear frontrunner, with rivals including a struggling Joe Biden and a re-invigorated Elizabeth Warren desperate to blunt the leftist firebrand's momentum.

Compounding the gravity, chilling warnings have emanated from Washington's intelligence community that Russia is interfering in the campaign, much as it did in 2016 when it sought to boost Trump's candidacy.

Democratic presidential hopeful Senator Elizabeth Warren, whose cardboard cutout proved a hit at her Las Vegas field office, claimed a fundraising bump after her standout debate performance ahead of Nevada's caucuses
Democratic presidential hopeful Senator Elizabeth Warren, whose cardboard cutout proved a hit at her Las Vegas field office, claimed a fundraising bump after her standout debate performance ahead of Nevada's caucuses AFP / Mark RALSTON

Trump, who was impeached in December over accusations that he tried to coerce ally Ukraine into helping him win the 2020 election, reportedly erupted in anger about a congressional briefing on the threat and sacked acting Director of National Intelligence Joseph Maguire.

In a fresh twist, The Washington Post reported that Sanders was told by US officials that Moscow is trying to help his campaign, efforts Sanders said he strongly rejects.

"My message to (Russian President Vladimir) Putin is clear: Stay out of American elections," Sanders said.

Eager to steal some of the Nevada spotlight, Trump held a raucous campaign rally Friday in Las Vegas, where Democratic candidates were converging for 11th-hour rallies of their own.

Former New York mayor Michael Bloomberg (L) and former vice president Joe Biden are two establishment candidates seeking the 2020 Democratic presidential nomination
Former New York mayor Michael Bloomberg (L) and former vice president Joe Biden are pictured at a 2020 democratic primary debate. AFP / Mark RALSTON

Trump lit into the "sick" Democrats who seek to oust him from power.

He reserved his harshest criticism for fellow New York billionaire Bloomberg, whom he mocked for his rough debate performance on Wednesday -- his first showdown with other Democrats since jumping into the race last November.

"I think he's gone," Trump said dismissively. "But you know what, he'll spend another $500 million."

Bloomberg has already spent a staggering $364 million, a campaign record, on advertising, according to Advertising Analytics.

US Senator Bernie Sanders, a leftist firebrand, leads in the race for the Democratic presidential nomination, and polling showed he is likely to win Nevada, which votes on February 22
US Senator Bernie Sanders, a leftist firebrand, leads in the race for the Democratic presidential nomination, and polling showed he is likely to win Nevada, which votes on February 22 AFP / RINGO CHIU

For some, Nevada -- or South Carolina, which votes on February 29 -- is a make-or-break moment before the race goes national on "Super Tuesday" on March 3, when 14 states vote.

Several contenders are facing fundraising hurdles and Nevada or South Carolina could be the end of the road.

Bloomberg chose to unconventionally skip the first four nominating contests and flood Super Tuesday states with advertising.

Rivals have revolted against the big-money tactic.

US President Donald Trump attacked "sick" and "crazy" Democrats on the eve of Nevada's vote in the process to determine the party's presidential nominee
US President Donald Trump attacked "sick" and "crazy" Democrats on the eve of Nevada's vote in the process to determine the party's presidential nominee AFP / JIM WATSON

"We are a democracy. One person, one vote -- not a guy worth $60 billion buying an election," Sanders fumed in a CBS interview.

Sanders added that he was surprised at Bloomberg's ineffective debate performance, when the media tycoon suffered a full-on assault from rivals.

Should Bloomberg -- currently third in national polling behind Sanders and Biden -- become the nominee, Sanders warned, "Trump will chew him up and spit him out."

Warren, whose campaign sagged after mediocre showings in Iowa and New Hampshire, eviscerated Bloomberg during the debate, leading to a much-needed injection of donations -- more than $5 million since the event, she said.

"I'm going to fight like hell to build a country that works for everyone," Warren said Friday.

Her debate attacks highlighted the non-disclosure agreements (NDAs) that Bloomberg has with women who have accused him of misconduct.

With polling by Morning Consult showing Bloomberg losing ground, from 20 percent support before the debate to 17 percent after, the media tycoon addressed the issue head-on.

In a tweet, Bloomberg said his company had identified three NDAs "signed over the past 30+ years with women to address complaints about comments they said I had made."

The women would "be given a release" if they ask, he said.

One candidate under tremendous pressure to turn his sinking campaign around is former vice president Biden, who performed dreadfully in the opening contests.

Biden must bounce back in Nevada and then South Carolina, two states with diverse demographics, if he wants to show he is still a contender.

Nevada's voting format is a caucus. Unlike a primary, where voting is by secret ballot, caucusgoers attend precinct gatherings where they vote publicly by standing with fellow supporters of their chosen candidate.

That process in Iowa devolved into chaos when online applications malfunctioned.

"What happened in Iowa will not happen in Nevada," the state's Democratic Party chairman William McCurdy declared on CNN.

Precinct captains and volunteers have been trained on what McCurdy called "low-tech" programming used to collate and transmit votes to party officials.