The night before the biggest assignment of her life, Usha Vance stayed up late with her husband, JD Vance. In their rooms at the Pfister Hotel in Milwaukee, they went over each other’s speeches to the Republican National Convention. She gave notes on his, and he tweaked hers.

In keeping with many intellectual and professional endeavors over the course of their relationship, which got its start at Yale Law School more than a decade ago, they approached the task as a couple.

Their lives were about to undergo a dramatic change. Two days earlier, former President Donald J. Trump had announced the selection of Mr. Vance as his running mate on the Republican presidential ticket. Mr. Vance was used to the spotlight, having made his name as the best-selling author of the memoir “Hillbilly Elegy” years before he was elected to the United States Senate in 2022, but his wife had remained largely a private figure.

Whatever nerves the self-possessed Mrs. Vance might have been feeling, she had allies bolstering her confidence. In the hours before she stepped onto the stage, a longtime friend texted her a trailer from “Bring It On,” the 2000 movie about highly competitive cheerleaders that was filmed in part at the high school she attended in San Diego.

Standing on the stage of Fiserv Forum before an audience of more than 17,000, with millions more watching on television, Mrs. Vance delivered a speech that was direct and conversational, without the theatrical bluster employed by many of her fellow convention speakers.

“When I was asked to introduce my husband, JD Vance, to all of you, I was at a loss,” she began. “What could I say that hasn’t already been said before? After all, the man was already the subject of a Ron Howard movie.”