Caro's book is full of innuendo and a bad attempt at a smear job. Johnson was helping out black colleges and black people and latinos long before it was popular to do so, mostly outside of his Congressional district as well, where it did no good re votes or support, from the beginnings of his political career as a secretary for Senator, which is also in Caro's book. I have the whole series. Caro found no evidence of anything, as a reading of the book will demonstrate.
Left wing commies hate him for Viet Nam and resisting their commie masters' takeover of that country as well as stepping in to back Israel when the French bailed out of the ME, cutting off the Soviet Union's attempt to make it a satellite of theirs, and this also led to the defeat of their Arab client states in 1967 and 1973, which the Arabs blamed on the Soviets for not supplying them with the latest tanks and rockets, which was bullshit, they lost because they were stupid, but nonetheless the rift never healed, as as we know the Soviets collapsed in 1973, largely due to the effects of Johnson's policies in Viet Nam, Africa, and the ME. The Soviet's propaganda war against Johnson has been taken up by the false flag operatives on the right wing now, which is even more shallow and feckless than the European left's campaigns of the 1960's and 1970's.