Sen. Bernie Sanders has solidified his position as the front-runner in the Democratic primaries and will face his next test today in the Nevada caucuses — as rivals like former vice president Joe Biden and Sen. Elizabeth Warren hope for a much-needed boost to their troubled campaigns.

Sanders goes into Nevada after tying former South Bend, Ind., mayor Pete Buttigieg in the Iowa caucuses and narrowly winning the New Hampshire primary. He's also experiencing an uptick in the polls that has separated him from the rest of the field.

In surveys conducted since New Hampshire voted, Sanders is averaging about 27 per cent support among Democratic primary voters. That puts him well ahead of Biden, who is at 17 per cent support, and former New York mayor Mike Bloomberg, at 16 per cent support.

That's a big shift in just the last 11 days: Sanders has averaged a four-point increase among pollsters who were in the field before and after the New Hampshire primary. Bloomberg has picked up one point and Biden has dropped three.

But that is only part of a broader trend that has hurt Biden since his disappointing showing in the Iowa caucuses. Since then, Biden has averaged an 11-point drop in support. That cost him the lead in the polls he enjoyed in January. Bloomberg, up seven points since pre-Iowa polling, has been the biggest beneficiary but both Sanders and Buttigieg have also seen gains, picking up four points each.

Warren hopes for a post-debate boost

There is a chance, though, that the trend line could stabilize after Nevada. Bloomberg was generally seen to have delivered a very poor performance in Wednesday's debate, while Biden was largely given a passing grade.

With her direct and pointed attacks on Bloomberg, Warren stood out and has reportedly seen a surge in fundraising.

Her campaign desperately needs a shot in the arm after failing to make much of an impact in either Iowa or New Hampshire. She is averaging just 12 per cent in the polls nationwide, putting her only narrowly ahead of Buttigieg's 10 per cent.

Rounding out the field are Sen. Amy Klobuchar (at six per cent), billionaire Tom Steyer (three per cent) and Rep. Tulsi Gabbard (one per cent).

With 23 delegates, Buttigieg currently has two more than Sanders. But only 65 pledged delegates have been allocated so far; Nevada's 36 delegates are only a tiny next step toward the final tally of 3,979.

Polls favour Sanders in Nevada

As with Iowa and New Hampshire, Nevada's importance is not in the number of delegates at stake, but in what the results say about the broader race. The two first states put serious question marks on the Biden and Warren campaigns. Nevada could provide some answers.

The third state to vote in the race for the Democratic nomination, Nevada has a demographic profile that makes it look a lot more like the rest of the United States than either Iowa or New Hampshire, two overwhelmingly white states. It is the first diverse state to cast a ballot — and the impact of the Latino vote in particular could prove decisive.

Since disappointing showings in Iowa and New Hampshire, former vice president Joe Biden's support has dropped in the polls significantly. He is now vying for second place with former New York mayor Mike Bloomberg. (Matt York / Associated Press)

The polls suggest Nevada could give Sanders his first outright victory of the primaries. He is averaging about 31 per cent support in the state, putting him well ahead of Biden's 15 per cent. The rest of the field is not far behind, with Buttigieg at 14 per cent, Warren at 13 per cent, Steyer at 12 per cent (he has outspent his rivals on advertising by a wide margin) and Klobuchar at eight per cent.

A few caveats on these numbers follow. While all the more reputable surveys have put Sanders in first place, second place has been awarded to Biden, Buttigieg or Warren, depending on the poll. Nearly all of these surveys were conducted before Wednesday's debate — an event which may have had an impact on voting intentions.

Why Nevada could matter

Nevada is also a caucus state, which means its voting method is far more complicated than a primary (see: Iowa) and harder to poll. Any candidate that is unable to earn 15 per cent support in a given precinct will see their voters redistributed to other candidates. That threshold could prove problematic for every candidate other than Sanders, since he's the only one polling comfortably above that level.

Biden, whose decline in support coincided with a rise in Bloomberg's, could benefit from the fact that Bloomberg is not contesting the state. He also could receive a boost from the local unions, which hold a lot of sway in the Nevada caucuses. If he manages it, a second-place showing could revive his flatlining third bid for the presidency.

Sen. Elizabeth Warren has dropped to fourth place in the polls nationwide and could struggle to win delegates in the Nevada caucuses without a significant boost from Wednesday's debate. (John Locher / Associated Press)

For Warren, a bump from the debate to over 15 per cent could help keep her campaign alive. Warren has been squeezed out by Sanders; both candidates have been targeting the same progressive slice of the Democratic electorate, and Sanders has been winning it so far.

If Warren falls below the threshold in precincts across Nevada, however, Sanders could benefit most from the re-allocation — a recent poll found Sanders was the second choice among Warren voters over Biden by a margin of nearly three-to-one nationwide.

The possibility of an upset of some kind shouldn't be discounted (they're not infrequent in U.S. primaries). Surprising results are the kind of thing that can shift the narrative in an important way, as they did for Buttigieg after Iowa. A third surprise could finally put him among the front-runners.

If Sanders fails to score a decisive win in Nevada, the more moderate candidates can continue hoping they can catch up. An unexpectedly strong showing by any of them could pay dividends in next Saturday's South Carolina primary and the Super Tuesday round of voting on Mar. 3.

Increasingly, though, Sanders' odds of winning the most delegates (if not necessarily the majority) are looking better and better. Nevada could be the latest sign of that, with implications that could cascade into votes further down in the calendar.

Whatever the results are, what happens in Nevada probably won't stay in Nevada.