what does "the lawyer who had been John Kennedy's mean?" actually I don't understand that sentence.
The question he had asked of the Congressmen was constitutional, which meant that the buck couldn't stop here on the plane. It had to go to the Department of Justice. Conceivably Deputy Attorney General Katzenbach could have been consulted; equally conceivably, Katzenbach would have checked with Kennedy anyhow. Thus the issue had to be laid before the lawyer who had been John Kennedys, and who was now automatically his successor's, Attorney General. That he should be the dead President's brother was cruel mischance, yet if the incoming Chief Executive were to exercise Tyler's "greater caution he had no option. Seated at the end of Jacqueline Kennedy's bed, with Rufus Youngblood standing against the wall, he accordingly placed a call to Robert Kennedy in Virginia, and moments later the white phone at the shallow end of Hickory Hill's swimming pool rang.