A few weeks ago, Hillary Clinton thought the Nevada caucuses were hers to lose. After a razor-thin victory in Iowa and a decisive loss in New Hampshire, Mrs. Clinton was counting on Nevada and South Carolina as a firewall to stop rival Bernie Sanders' momentum.

That firewall appears to be crumbling.

Some 48 percent of likely Nevada caucus-goers say they will support the former Secretary of State, while 47 percent say they will support Senator Sanders, according to a new CNN/ORC poll.

Other polls show the candidates locked in the same dead heat: Clinton is up just 44 percent to Sanders' 42 percent in the latest Quinnipiac University survey, while TargetPoint shows them in a flat tie, 45-45, and forecasting blog FiveThirtyEight's weighted polling average shows Clinton edging Sanders 47-45.

The close race is a surprise, to the say the least, and a lot is riding on the outcome. If, as was originally expected, Clinton wins Nevada, she may yet stop Sanders' momentum, confirm fears that he is weak with minorities, and resume her narrative of electability in South Carolina and beyond.

If, however, Sanders wins, or even if it's another razor-thin tie as in Iowa, the race may be redefined.

A tie or a Sanders win will prove the Vermont senator is more than a single-issue candidate unknown to minorities, and will call into question Clinton's central argument, that she is the only electable candidate with broad appeal.

The Nevada caucuses, then, are pivotal. Here are three factors that determine who wins.

Turnout

In a nutshell, a higher turnout helps Sanders, while a lower turnout helps Clinton. That's because Sanders is more likely to do well with first-time caucus-goers and those who are not regular participants in the caucus process. Clinton fares better with those who are definitely going to participate and who have participated in the past.

As it stands, 62 percent of Nevada Democratic caucus voters said they have definitely decided who they will support, while 38 percent said they were leaning toward someone or still trying to decide.

This is a particularly ambiguous situation in a state such as Nevada that allows same-day registration and may allow a lot of new Sanders voters to change the course of the election.

"Thirty thousand new voters registered on Caucus Day in 2008," writes veteran Nevada political writer Jon Ralston. "No one expects it to get that high Saturday, but that uncertainty is what makes polling so difficult and nervousness so prevalent in Clintonland."

It's the economy, stupid

If there's one issue this race hinges on, it's the economy, currently rated as the top issue by 42 percent of likely Democratic caucus goers.

When it comes to which candidate performs better on this issue, the race is evenly split. On who would better handle the economy, 48 percent said Clinton and 47 percent said Sanders.

Among those likely caucus goers who call the economy their top issue in choosing a candidate, however, more support Sanders: 52 percent, compared with 43 percent for Clinton. And when asked who would do more to help the middle class, Sanders narrowly tops Clinton among all likely caucusgoers, 50 percent to 47 percent.

Clinton is feeling the pressure. In recent campaign events, she appeared to be trying to erode Sanders's support on the economy by suggesting he is a single-issue candidate.

"Not everything is about an economic theory, right?" Clinton asked a crowd Saturday in Henderson, Nev. "If we broke up the big banks tomorrow – and I will, if they deserve it, if they pose a systemic risk, I will – will that end racism?"

"Will that end sexism? Will that end discrimination against the LGBT community? Will that make people feel more welcoming to immigrants overnight?" Clinton asked. "Would that solve our problem with voting rights and Republicans who are trying to strip them away from people of color, the elderly, and the young?"

Demographics

As was clear from his virtual tie in Iowa and landslide win in New Hampshire, both overwhelmingly white states, Sanders does well with white voters. National polling suggests Clinton performs better with minorities, who should be well represented in Nevada. Clinton also has an edge with women and older voters, while Sanders performs well with voters under 55.

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In 2008, the Nevada Democratic caucus electorate was roughly 65 percent minority, a level that would benefit Clinton. But in the past few days, her team has worked to lower expectations. They recently claimed turnout is expected to be 80 percent white, which would put it near Iowa and New Hampshire levels – and almost certainly benefit Sanders.

"This was not only visibly false, but a clear sign that she wasn’t just lowering expectations but showing real fear she could lose Nevada," says Mr. Ralston. "The Clinton panic is palpable."