New Hampshire voters will make their choice for president today.
Polls suggest that Republican Donald Trump and Democrat Bernie Sanders are favorite to win the state’s voters.
Polls will open across most of the state at 8 a.m.
Big questions could be answered once the results roll in later Tuesday. 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.
Republican front-runner Donald Trump is in for a nervous night 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.
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.
Trump hinted Sunday that he understands how crucial New Hampshire is to his campaign. "I could say to you if I came in second and third I'd be thrilled, okay? I know all about expectations," Trump told CNN's Dana Bash on Sunday. "If I came in second I wouldn't be happy, okay?"
Bush, who for once equaled or even got the better of Trump on the debate stage on Saturday, has been mounting a last stand in New Hampshire and on Monday lashed out at the former reality TV star on Twitter.
"You aren't just a loser, you are a liar and a whiner," Bush wrote in an apparent reference to Trump's claims of irregularities in the Iowa caucus results.
Trump had a scathing response in an interview with CNN's Wolf Blitzer: "He's a stiff. He's not a guy that can be president. He doesn't have what it takes." He continued, "He's a desperate person. He's a sad and, you know, he's a pathetic person. He doesn't even use his last name in his ads. He's a sad person who has gone absolutely crazy. He's a nervous wreck."
The Democratic race between Clinton and Sanders also got testy, with a clash over the former New York senator's ties to Wall Street and her campaign's attacks on his foreign policy.
On Sunday, Bill Clinton slammed the Vermont senator's supporters who he said subjected opponents to "vicious trolling and attacks that are literally too profane often -- not to mention sexist -- to repeat."
Only hours from the primary, new clouds gathered around the Clinton campaign following a Politico report that the candidate and her husband were disappointed with the direction of her campaign and that a staff shakeup could be in the offing.
But Clinton campaign chairman John Podesta dismissed the report. "There is zero truth to what you may be reading. It's wrong. Hillary stands behind her team, period," he wrote on Twitter.
