Polls will opened across most of the Granite state at 8 a.m. ET, though a trickle of voters made it to the polls in the traditional curtain raiser of Dixville Notch not far from the Canadian border just after midnight. In that snow-bound hamlet, Ohio Gov. John Kasich bested Trump 3-2 among Republicans, while Sanders claimed all four votes among Democrats.

A cluster of big questions could be answered once the results roll in later Tuesday after a week of frenzied campaigning. The contest follows last week's Iowa caucuses where Texas Sen. Ted Cruz had a clear win and Democrat Hillary Clinton barely edged out Sanders.

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Trump is in for a nervous day as he waits to see whether he can turn support at huge rallies into votes after falling short of his polling numbers in Iowa last week.

Marco Rubio's stumble under New Jersey Gov. Christie's ferocious fire at Saturday's GOP debate, meanwhile, threatens to stall his momentum heading into New Hampshire, where the Florida senator looked likely to emerge as the top establishment candidate.

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For their part, Democrats are waiting to assess the magnitude of Sanders' expected victory over Clinton, which could offer the anti-Wall Street crusader a boost heading into less hospitable territory in southern states.

Campaigning for the primary drew to a close Monday with Trump and former Florida Gov. Jeb Bush trading deeply personal taunts and Rubio trying to bounce back from his tough debate night.

The latest CNN/WMUR daily tracking poll on Monday showed Sanders with a 26-point lead over Clinton. On the Republican side, Trump maintained the lead he has held for months, 31% to next-best Florida Sen. Rubio with 17%. Three-quarters of the polling was completed before Saturday's debate, so it was unclear whether Rubio had been hurt by his rocky performance.

Among other candidates, Cruz was third with 14%, ahead of Ohio Gov. John Kasich at 10% and former Florida Gov. Jeb Bush at 7%. Christie received 4%, according to CNN's tracking poll. The survey has a margin of error of plus or minus 5.2 percentage points. The high number of undecided voters could make this a very fluid race.

Despite his lowly position in the polls, Christie has spent the past few days basking in his debate assault on Rubio.