US Republican presidential candidate Donald Trump says he does not have to win the New Hampshire primary vote to secure the nomination, apparently tamping down expectations despite holding a double-digit lead in that state's polls.

The billionaire businessman came second to Texas Senator Ted Cruz in the Iowa caucuses last week although polls put him ahead.

His candidacy has alarmed the Republican establishment and has been marked by rows, including over his calls for a temporary ban on Muslims entering the United States.

No Republican has won the presidential nomination without winning either the Iowa caucuses or the New Hampshire primary since the 1970s, but it would not technically be impossible.

Asked whether a loss in New Hampshire on Tuesday would derail his campaign, Trump told the NBC News show Meet the Press: "I don't think I need it. I hope that I get it."

"I would like to win, but I don't know that it is necessary."

Recent opinion polls give him a lead of between 10 and 22 percentage points over the next closest contender.

Trump has built his campaign in part around his self-declared reputation as a "winner", and a loss in New Hampshire would intensify doubts that he can translate opinion poll support into votes.

He also told Meet the Press that he has spent as much as $US50 million ($A70 million) less than expected on the campaign so far, in part because the media provides him so much free publicity.

"People like you put me on. What do I take a commercial for?" Trump told the show's moderator Chuck Todd.