DELAVAN, Wis. — Who could have guessed in the mid-1980s, at a pair of otherwise forgettable McDonald’s restaurants some 20 miles apart, that two bushy-haired teenagers working the burger grills would become Wisconsin’s most powerful Republicans?

Scott Walker, 47, now the governor and a likely presidential candidate, was a record-setting track star with a mean mullet when he donned the McDonald’s uniform — black pants, white shirt, long black tie — to make Big Macs here in his hometown.

Paul D. Ryan, 45, now a powerful United States representative who was the Republican vice-presidential candidate in 2012, suited up with something greater in mind in nearby Janesville: operating the front register. One dark day, though, Mr. Ryan’s manager told him that he lacked the “interpersonal skills” to deal with customers — and into the kitchen he went.

Mr. Walker tells that story of a young Mr. Ryan to virtually every Republican crowd he meets as he prepares for his campaign for president, sprinkling his biography with some of the gold dust Mr. Ryan has accrued as a favorite of conservatives — and as the better-known name, from his three months as Mitt Romney’s running mate.