“Before Ted was 10,” his father says, “he was jumping into our dinner-table conversation about replacing the leftist government of Jimmy Carter with a constitutional conservative like Ronald Reagan.”…

At Princeton, he showed up as “much the same person he is today,” says Mr. Panton, his former roommate, now an Atlanta investor. “Surrounded by liberals, Ted was resolute with his conservative principles,” he says. “Even in the dorm room, he talked about Ronald Reagan all the time.”

Mr. Cruz admits to some youthful indiscretions. At Princeton, he built up a $2,000 debt playing poker and had to borrow from his aunt to pay it off. At Harvard, he acted in “The Crucible” but was once so hung over he had to leave the stage.

His Reagan obsession permeated his personal life. Before his marriage ceremony, he took the wedding party for a picnic at the Reagan ranch.

“I grew up in a nonpolitical, Patagonia-wearing, mountain-climbing, vegetarian family in California,” Mrs. Cruz says of her courtship. “And then I fall in love with a Hispanic man from Texas who loves the game of politics, is a policy wonk, and…lives and breathes the values of Ronald Reagan.”