Chris Sununu, Nikki Haley’s ‘Best Friend,’ Won’t Stop Believing

As he introduced Nikki Haley at a bar in Milford, N.H., Gov. Chris Sununu of New Hampshire was in a comfortable place — surrounded by a swarm of media cameras and local voters.

“Oh my goodness, this thing is hot,” he said into the microphone as his voice cracked in the speakers. He gave a whirlwind recap of his day crisscrossing the state with Ms. Haley and urged supporters to vote before passing the mic. “I’m going to turn it over to the star,” he said. “I’m just the lowly governor today. I’m the sherpa, as I like to say.”

Most endorsements of presidential candidates follow a standard path: a leaked announcement, a big speech in the spotlight and occasional introductions at events. Mr. Sununu’s endorsement of Ms. Haley has not been like most endorsements.

Part hype man, part campaign aide, part spokesman, part surrogate, part “new best friend” (his words), Mr. Sununu has been omnipresent on Ms. Haley’s campaign.