"When we win the presidency in this country, I will do everything I can to prove to you that you made the right decision," she told her supporters. "For now, I'll leave you with this: may the best woman win."

DeSantis, the governor of Florida, ended his White House bid on Sunday, two days before the New Hampshire primary. His exit leaves Haley as Trump's sole challenger for the GOP nomination.

However, he has since also endorsed Trump for the presidency, adding to Haley's uphill battle against the former president, who has a loyal and passionate following and a huge fundraising advantage.