When Nikki Haley conceded her deflating third-place defeat in the Iowa caucuses this month, the first person she thanked was nearly 8,000 miles away.

“I want to say to my husband, who is deployed, who I know may or may not be watching this right now — Michael, I love you,” she said, standing in front of a row of American flags. “What keeps me going at night is that we sleep under the same stars.”

It was an unusually personal and almost saccharine note for a politician known for her tough exterior. But it was hardly out of place.

Even in his absence, Maj. Michael Haley, a National Guardsman serving a voluntary, yearlong deployment in Africa, has played an outsize role in his wife’s increasingly lonely attempt to snatch the Republican nomination from former President Donald J. Trump.

In nearly every stump speech, Ms. Haley describes her husband and his military career as one of her motives for running. She frequently refers to his struggles after returning from a war zone in her promises to improve health care for veterans. She suggests that his work has informed her foreign policy.

Yet, despite this prominence, Major Haley himself remains something of a blank slate. While other candidates’ spouses — with the notable exception of Melania Trump — logged miles across Iowa and New Hampshire last year trying to humanize their other halves, he has avoided the intense scrutiny, as well as the public speaking, photo ops and interviews, that comes with campaigning.