O'Reilly has never gotten over his Irish Catholic Democrat upbringing in Levittown. He even said in Killing Kennedy that families like his all had a portrait of Kennedy in their homes and regarded him as a near-saint. He went on in the book to excuse all of the reckless, smartass Kennedy's terribly bad judgment in Bay of Pigs, extramarital affairs covered up by the press, pissing off scores of pressure groups who would want to have him killed, etc., and even as a ghost-written biographer who calls himself an historian, O'Reilly could never let go of worshipping Kennedy. A very disappointing book for me, after having very much enjoyed Killing Lincoln.
You nailed it. His formative years, he's never grown out of them.