MIAMI—Former South Carolina Gov. Nikki Haley, who has shown momentum in recent weeks, came under sustained attack in Wednesday’s Republican presidential primary debate as she competes with Florida Gov. Ron DeSantis to be the leading alternative to former President Donald Trump.

She also delivered several of her own shots at DeSantis, who tried to float above the fray, but engaged with her on China, energy policy and a handful of other issues. A confrontation between the two had been brewing, amplified by a closely watched poll that recently showed Haley and DeSantis tied for second in Iowa, where nomination balloting starts Jan. 15.