Seven Republicans seeking the party’s nomination to run for the White House are due to return to the stage in the latest TV debate.
Ted Cruz will be looking to build on his victory in the Iowa caucuses ahead of the New Hampshire primary election.
Controversial billionaire Donald Trump will be looking to mount a comeback after his second place finish in Iowa.
Marco Rubio came third in Iowa and is seen as a rising force, leading many of his rivals to question his credentials.
The other debaters will be former Florida Governor Jeb Bush, New Jersey Governor Chris Christie, Ohio Governor John Kasich and retired neurosurgeon Ben Carson.
The results of Tuesday’s New Hampshire primary are expected to determine whether or not some of the Republican candidates drop out.
ABC News, which is hosting the debate in Manchester, New Hampshire, has dropped an undercard event for low-polling candidates, leaving former Hewlett-Packard CEO Carly Fiorina as the only remaining candidate without a spot on stage.
The only woman candidate in the Republican field released an open letter describing the debate process as “broken.”
Mr Trump boycotted the final TV debate before the Iowa caucuses, and later demanded a re-run of the state vote after reports that supporters of Mr Cruz, a Texas senator, had told caucus-goers that Mr Carson was dropping out of the race.
The Cruz campaign later apologised to Mr Carson, saying it was a misunderstanding.
Voters will make their choice in both the Republican and Democratic races in New Hampshire on Tuesday.
More on the race for the White House
- Why are Americans so angry? The underlying forces that explain rise of Trump, Cruz and Sanders
- American exceptionalism in a time of American malaise How a phrase that once evoked glory now provokes derision
- Winners and losers after Iowa vote: How Republican Senator Marco Rubio placed third but still won
- How does a US election work? If you want to be president, it helps to be governor, senator, or five-star military general – and have lots of patience
- Special report: The BBC’s full coverage of the race to the White House