AP Decision Notes: What to expect in the South Carolina Republican presidential primary

WASHINGTON (AP) — Donald Trump and Nikki Haley will face off Saturday in South Carolina’s first-in-the-South Republican presidential primary, the first head-to-head matchup for the last two remaining major candidates since the New Hampshire primary a month ago.

The contest takes place on Haley’s home turf. She was South Carolina's governor for six years before stepping down in 2017 to serve as U.N. ambassador when Trump was elected president. Despite her history, Haley faces strong headwinds in a state where Trump has the support of most of the party establishment, has held a substantial lead in recent polls and enjoys high popularity among the conservative base.

Both candidates have made sharp attacks against the other, with Trump using derisive nicknames for Haley and playing down her work in his Cabinet. Haley has increasingly questioned Trump’s fitness for office, most recently criticizing his comments on Russia and NATO. It is a marked contrast from earlier in the campaign when she and other GOP hopefuls avoided criticizing Trump directly.

The South Carolina primary is usually an indicator of which candidate will win the Republican presidential nomination. Since the modern version of the state’s primary began in 1980, all but one GOP primary winner has gone on to win the party’s nomination. The lone exception was Newt Gingrich in 2012.