New Hampshire Gov. Chris Sununu endorses Nikki Haley

The big picture: Sununu, who mounted a brief presidential campaign himself, had been holding out on making an endorsement as he weighed which candidate was the best positioned to take on the former president.

• The popular New Hampshire governor has appeared with almost all of the Republican presidential hopefuls in recent months, CNN notes.
• Sununu, a vocal Trump critic, dropped out of the presidential contest in June and said at the time that he would have "more credibility speaking out against Trump ... to help move the conversation toward the future I believe the Republican Party should embrace."

Zoom in: Haley and Florida Gov. Ron DeSantis are vying for second in the Republican primary.

• Haley has earned endorsements from GOP establishment mega-donors in recent weeks, and she won the support of the politically powerful network backed by the Koch family.

Between the lines: The endorsement is a possible blow to former New Jersey Gov. Chris Christie, who has aggressively campaigned in New Hampshire.

• "We have seen the reports of Governor Sununu's decision to endorse Nikki Haley,” Christie spokesperson Karl Rickett said in a statement.
• "This puts us down one vote in New Hampshire and when Governor Christie is back in Londonderry tomorrow, he'll continue to tell the unvarnished truth about Donald Trump and earn that one missing vote and thousands more."

Go deeper: CNN's GOP debate in Iowa in peril

Editor's note: This article has been updated with comment from Karl Rickett, a spokesperson for Republican presidential primary candidate Chris Christie.