Republican presidential candidate, billionaire Donald Trump, gestures to the crowd as he signs autographs at a campaign event at Plymouth State University Sunday, Feb. 7, 2016, in Plymouth, New Hampshire.
Republican presidential candidate, billionaire Donald Trump, gestures to the crowd as he signs autographs at a campaign event at Plymouth State University Sunday, Feb. 7, 2016, in Plymouth, New Hampshire.

MANCHESTER, NEW HAMPSHIRE - Presidential hopefuls traveled across snowy New Hampshire on Monday, making a final appeal to undecided voters and stepping up their attacks on rivals, one day before an election that could make or break several candidates' White House aspirations.

Ahead of the vote, opinion polls in New Hampshire showed Vermont Senator Bernie Sanders with a shrinking but still comfortable double-digit lead over former Secretary of State Hillary Clinton in the Democratic race.

Outspoken businessman Donald Trump appears to be leading the rest of the Republican field by an even larger margin. Five or six mostly establishment candidates are in a closely watched battle to finish second behind Trump in the Granite State.

Last-minute sprint

A winter storm was sweeping across much of New Hampshire on Monday, dumping several centimeters of snow. But the storm did not stop the candidates from holding campaign events.

WATCH: VOA reporters talk about Democratic candidates

"For those of you who are still deciding, still shopping, I hope I can close the deal," said Clinton, appearing with her husband, ex-President Bill Clinton, at a rally in Manchester.

Sanders, a Democratic socialist who proposes drastically larger government welfare programs, also campaigned in Manchester, where he continued to rail against economic inequality.

"It is not right that millions of families are struggling just to send their kids to college. It is not right that our infrastructure is crumbling. It is not right that 29 million Americans have no health insurance and more are underinsured," Sanders said.

Sanders is expected to win in New Hampshire, which neighbors his home state of Vermont. Clinton continues to be ahead in most national polls, though Sanders has been coming up in recent weeks.

Trump, Bush exchange insults

Trump, the Republican frontrunner, spent much of Monday launching fierce personal attacks on ex-Florida Governor Jeb Bush.

"This stiff, Jeb Bush," Trump said at an event in Salem. "If you had a company, you wouldn't even hire him. He's like a child, a spoiled child."

The real estate mogul continued the fight on Twitter, where he called Bush "desperate," "weak," and "pathetic" for spending millions of dollars on ads in New Hampshire.

WATCH: VOA reporters discuss Republican candidates

Bush, who is relying on a strong showing Tuesday to revive his floundering campaign, shot back in a tweet, telling Trump: "You aren't just a loser, you are a liar and a whiner."

Make or break

Bush is one of several more moderate, establishment GOP candidates who appear to be placing their entire presidential hopes on New Hampshire, which has a more centrist population than Iowa, which held caucuses last week.

Republican presidential hopeful, Ohio Governor Joh
Republican presidential hopeful, Ohio Governor John Kasich meeting with voters at the Derryfield Restaurant in Manchester, New Hampshire, Feb. 8, 2016.(VOA/K. Gypson).

The group also includes New Jersey Governor Chris Christie, Ohio Governor John Kasich, and Florida Senator Marco Rubio.

Rubio, whose campaign appeared to be on the rise after a stronger-than-expected third-place finish in Iowa, is trying to recover from last week's shaky debate performance.

The freshman senator told CBS This Morning he feels he did "great" in the Saturday debate. "Despite what people want to say, it was our greatest fundraising night," Rubio said.

During the debate, Rubio awkwardly repeated the same criticism of President Barack Obama four times, using nearly the exact same words each time.

Rubio's rivals — particularly Christie, Bush and Trump — say the gaffe is proof the Florida lawmaker is not ready for the pressures of the presidency.

WATCH: VOA reporters talk about primary voters

Another candidate involved in the heated race for second place in New Hampshire is Texas Senator Ted Cruz.

Cruz won Iowa in large part with the support of evangelical Christians, but faces a tough challenge in New Hampshire, where the electorate is less religious.

Undecided voters

There is still a large amount of uncertainty headed into Tuesday's vote.

Only about half of Republican voters have "completely decided" on a candidate, according to a poll by Monmouth University. On the Democratic side, that figure inches up to about 60 percent.

Another reason for uncertainty is the state's undeclared voters — those who are neither registered Democrats or Republicans — who make up 44 percent of the electorate and who can vote in either party's primary.