The POD is that instead of assassinating RFK, Sirhan Sirhan tries to kill President Johnson as he initially planned to do in OTL. However, the attempt is foiled by the Secret Service and Sirhan goes to jail. Kennedy continues his presidential campaign and comes close to the nomination, but he narrowly loses to Vice President Humphrey at the convention.
Humphrey still loses in November (but perhaps does better due to butterflies) and Nixon takes office on January 20, 1969. How does RFK's career pan out during the Nixon years?