From 1996, when he left the pizza company, until 1999, Mr. Cain ran the National Restaurant Association, a once-sleepy trade group that he transformed into a lobbying powerhouse. He allied himself closely with cigarette makers fighting restaurant smoking bans, spoke out against lowering blood-alcohol limits as a way to prevent drunken driving, fought an increase in the minimum wage and opposed a patients’ bill of rights — all in keeping with the interests of the industry he represented.

It was a role that gave him an intimate view of the way Washington works, putting him in close proximity to Republican leaders at the time, including Newt Gingrich, now one of his presidential rivals, and John A. Boehner, now speaker of the House. And it helped Mr. Cain lay the groundwork for the next chapter in his life, his entry into electoral politics, beginning with a short-lived bid for the White House in 2000…

Mr. Cain did not entirely become a creature of Washington during his time here. He kept his home in Omaha, where the pizza company was headquartered, and took an apartment in the Northern Virginia suburbs. Weekdays, when he was not traveling, he worked out of the association’s Washington headquarters. Weekends, he flew home to his wife in Omaha.