NewsNation) — Republican New Hampshire Gov. Chris Sununu doubled down on his endorsement for GOP candidate Nikki Haley, calling her “the next generation of conservative leadership.”

Former President Donald Trump remains the front-runner in the Republican primary, polling at about 64%, according to Decision Desk HQ/The Hill polling averages.

Haley, however, is catching up to distant second contender Florida Gov. Ron DeSantis.

Nationally, Haley was polling around 10% and DeSantis at 11.1% as of Thursday. Fellow candidates Vivek Ramaswamy and Chris Christie were polling about 4.2% and 2.7%, respectively.

“When those Chris Christie voters come to Nikki Haley, she’s literally tied with Donald Trump, and that’s something no one in the national media thought could happen anywhere at any point in this election, but that’s the reality that’s coming,” Sununu said Thursday during “NewsNation Now.”

Although some have described Haley’s views as more moderate, Sununu said he has no doubts the former South Carolina governor is a “strong conservative.”

Trump called Sununu a “spoiled brat” during a rally Saturday in Durham, New Hampshire, days after Sununu endorsed Haley.

Sununu responded to Trump’s criticism Monday on “CUOMO,” saying the former president is worried about Haley’s recent rise in the polls.

That’s one of the reasons why, Sununu said, Trump is using “extreme rhetoric” to galvanize his base.

Trump’s repeated comments that immigrants are “poisoning the blood of our country” have been criticized as being xenophobic and rooted in Nazi rhetoric.

“(Trump) knows Nikki is gaining traction,” Sununu said. “He knows she’s the only one with momentum. So he’s panicked that if he doesn’t galvanize and stir up the anger among his base, he could potentially lose them.”