Thomson Reuters
Republican U.S. presidential candidate Donald Trump talks to Senator Rubio.
The debate could be a last stand for many of the establishment-minded candidates in the field - including former Florida Gov. Jeb Bush (R), Ohio Gov. John Kasich (R) and New Jersey Gov. Chris Christie (R). They have all invested significant resources in the Granite State.
Most of those candidates' fire this week has been aimed at Sen. Marco Rubio (R-Florida), who has been surging after his stronger-than-expected, third-place finish in the Iowa caucuses.
The one candidate who hasn't directed many shots at Rubio this week has been real-estate magnate Donald Trump, who remains the front-runner in New Hampshire even after his second-place finish in Iowa.
Instead, he has spent much of the week feuding with Sen. Ted Cruz (R-Texas), the winner of the Iowa caucuses, who he has said "stole" the victory there. The charge stems from messages delivered by Cruz campaign staffers on caucus night that said retired neurosurgeon Ben Carson was "suspending campaigning," among other things - when, in fact, Carson's campaign said he was simply flying from Iowa to Florida to get a "fresh pair of clothes."
The Cruz and Carson campaigns have been feuding about the incident for much of the week.