Though Rabbi Boteach now criticizes Mr. Booker’s Hebrew citations as a “parlor trick,” they are warmly welcomed by many Jews, from the Orthodox to secular. (Many of Mr. Booker’s Jewish donors say, only half-jokingly, that he knows more about the religious tradition than they do.)

“There’s a twinkle that’s coming from his soul,” said Rabbi Shmully Hecht, with whom Mr. Booker worked to create a Jewish group at Yale. He also criticized Mr. Booker’s vote on Iran, but considers him a steadfast supporter of Israel. “When you see him talking about Jewish things and Israel things, it’s extraordinary.”

Rabbi Menachem Genack, who leads the kosher certifying division of the Orthodox Union and lives in Englewood, N.J., met Mr. Booker through Rabbi Boteach more than two decades ago and has considered him a friend ever since. Rabbi Genack, who published a book of his letters to former President Bill Clinton, said it is often Mr. Booker who brings up Torah in their conversations.

“I go to his office and I start talking Abraham Lincoln and he starts talking about the parsha,” said Mr. Genack, using the Hebrew term for the weekly Torah portion. “I say: ‘Cory, what is wrong with this picture?’ and he just laughs.”

Several years ago, Rabbi Genack brought the chief rabbi of Israel to meet Mr. Booker at his office. Soon after the conversation began, Mr. Booker pulled out a special coin of Rebbe Menachem Schneerson, the founder of the Chabad-Lubavitch movement. He said that he kept it in his pocket for years as kind of a talisman, but after a few scares, he began leaving it on his bedside nightstand. Now, he carries a blue index card with a quote from the prophet Isaiah. “But they who trust in the Lord will renew their strength. They will soar on wings like eagles; they shall run and not grow weary, they shall walk and not grow faint.” Ever ecumenical, he also keeps a saint card, with a prayer written in Spanish.

“I think of Cory as Jew-ish,” said Eric Garcetti, the mayor of Los Angeles who was a Rhodes Scholar with Mr. Booker, and spent time with him at the L’Chaim Society, where Mr. Booker would regularly share his insights on Jewish texts. (Mr. Garcetti, who is Jewish, now regularly studies with a rabbi himself.) “It’s a thread in the fabric that sustains him. Civil rights history and the Talmud are two main pillars of his moral universe. He understands the Jewish base of Christianity, of how Jews were such critical figures in the civil rights movement.”

Mr. Booker has frequently spoken about how a Jewish lawyer helped his parents settle in what was an overwhelmingly white suburb. He said he does not see his interest in Judaism as in conflict with his own faith, and instead has used it to deepen his own private prayer. Mr. Booker has never indicated any interest in converting, said Noah Feldman, now a law professor at Harvard, who has been close with the senator since their time at Oxford and later at Yale Law School, where the two helped create another Jewish student organization.