Doug Emhoff is a contender to become the country’s first Second Gentleman.

Doug Emhoff, who emerged as a fervent professional spouse during Senator Kamala Harris’s thwarted campaign for the Democratic nomination for president, is a serious contender to be the country’s first-ever Second Gentleman.

Only two women besides Ms. Harris have ever been nominated for the vice presidency from major parties, so Mr. Emhoff finds himself in a rarefied club. His predecessors include John Zaccaro, a real estate developer whose complicated financial arrangements and reluctance to release his tax returns tarnished his wife, Geraldine Ferraro, Walter F. Mondale’s running mate in the 1984 election. And there was Todd Palin, the rough-and-ready snowmobile-racing “first dude” of Alaska, whose wife, Sarah Palin, was the running mate of Senator John McCain in 2008, hampering his candidacy. (The Palins are now divorced.)

Mr. Emhoff, a partner at the law firm DLA Piper who specializes in media, sports and entertainment litigation, and Ms. Harris, both now 55, married in 2014 — his second marriage, her first.

Husbands of high-profile candidates walk a tricky line, required to exude both alpha-male independence and second-wheel supportiveness, said Lori Poloni-Staudinger, a professor in the politics and international affairs department at Northern Arizona University whose work focuses on women and politics. “There’s a fascination with women candidates’ domestic lives that we don’t see with men’s lives,” she said.