Backgrounder: What to expect from New Hampshire presidential primary?

The first-in-the-nation primary will kick off in New Hampshire on Tuesday with smaller but still wide open fields in both Democratic and Republican parties eight days after the Iowa caucuses.

For decades, the New Hampshire primary, along with the Iowa caucuses, the first-in-the-nation caucuses, has been the place for candidates to "test the water" of the presidential election.

Different from the complex caucus system that Iowa adopts to pick its favored presidential candidate, the New Hampshire primary is much more straightforward with voters casting secret ballots statewide.

And unlike the Iowa caucuses organized by political parties, the primary is run by the New Hampshire secretary of state's office. Thus, the vote can be recounted if necessary.

In this year, the actual vote will be held statewide on Tuesday, and most voting locations will open from 7 a.m. to 7 p.m. local time. However, in Manchester, the state's biggest city, polls are open from 6 a.m. to 7 p.m. local time.

In the past election cycles, New Hampshire voters were famous for high turnout.

In the 2012 primary elections, 31.1 percent of eligible New Hampshire voters showed up while turnout rates for the majority of U.S. states ranged from less than 1 percent to 20 percent at most, according to data offered by United States Elections Project.

Despite a predicted snowstorm on Tuesday here, the turnout rate is expected to surpass that of 2012 here with both Democratic and Republican fields being competitive. According to New Hampshire Secretary of State Bill Gardner, a record 550,000 votes will be cast on Tuesday.

Also, for the first time in this election cycle, the Republican field has finally shrunk to under 10 candidates, with New York billionaire developer Donald Trump continued to top the rest of the Republican field.

However, Trump's win in New Hampshire is not guaranteed, with Florida Senator Marco Rubio, the runner-up in the Iowa caucuses, surging to the second place.

For the crowded "establishment lane," however, the New Hampshire primary has become a fight for survival, with former Florida Governor Jeb Bush, Ohio Governor John Kasich, New Jersey Governor Chris Christie struggling to seek a big win to justify continuing their campaigns into South Carolina.

On the Democratic side, after her razor-thin edge over Bernie Sanders in the Iowa caucuses, Hillary Clinton is expected to face an uphill battle in courting New Hampshire voters, a constituency which in 2008 helped her to defeat Barack Obama after her loss in the Iowa caucuses.

For weeks, Sanders had enjoyed a decisive edge over Clinton in the polls and the latest NBC News/Wall Street Journal/Marist poll on Thursday found Clinton was trailing Sanders by 20 percent.

With lopsided support among young people and independents, Sanders, a U.S. senator from neighboring state Vermont, garners 58 percent support from likely Democratic primary voters in New Hampshire, with Clinton receiving 38 percent support, said the poll.

However, due to a large number of undeclared voters in the state -- about 44 percent according to a poll -- and the fact that those independents can vote here in either party's primary, any prediction based on pre-primary polls here is unreliable.

In 2008, undeclared voters indicated a preference for then Senator Obama, Clinton ultimately won the New Hampshire primary with more support from registered Democrats. Endit