Here are my strong contenders:
- Byron White, had meet JFK while they were in England, and was the Colorado state chair of John F. Kennedy's 1960 presidential campaign, would IOTL serve as 4th United States Deputy Attorney General and then Associate Justice of the Supreme Court of the United States. He studied University of Colorado, Boulder (BA) Hertford College, Oxford Yale University (LLB).
- Estes Kefauver, vice presidential candidate in 1956, United States Senator from Tennessee since 1949, been in congress since 1939. A southern lawyer gives him credit from the south. Has a Bachelor of Laws degree from Yale Law School, between 1927 and 1939, Kefauver practiced law in Chattanooga, first with the firm of Cooke, Swaney & Cooke, as a partner in Sizer, Chambliss & Kefauver, and later in the firm of Duggan, McDonald, & Kefauve. Kefauver refused to sign the Southern Manifesto, he faced staunch opposition for renomination from his party's still-thriving pro-segregation wing, but he won the primary decisively, 64% vs. 34% for his opponent, Tip Taylor. Hopefully, working in the cabinet, would make him stop smoking and drinking heavily.
- Thurgood Marshall, IOTL Associate Justice of the Supreme Court of the United States (1967-1991) as the first African-American justice. Marshall was a lawyer who was best known for his high success rate in arguing before the Supreme Court and for the victory in Brown v. Board of Education, a 1954 decision that ruled that segregated public schools were unconstitutional.
- Adlai Stevenson II, Presidential candidate in both 1952 and 1956, former-governor of Illinois. IOTL served as U.S. Ambassador to the United Nations from 1961-1965, recieved a Bachelor of Laws at Northwestern University School of Law, obtained a position at Cutting, Moore & Sidley, an old and conservative Chicago law firm.
- Hubert Humphrey, more of an ally of Johnson, he is an avid speaker on actively protect civil rights for racial minorities
- Arthur Goldberg, would later serve JFK as U.S. Secretary of Labor and Supreme Court Justice.