I'm not very good with history but I wonder when this first started. I would speculate LBJ was a driving force behind catering to the special interest which he was well known for. From there it must have escalated.
The 1960s were where the foundation was built but not really with LBJ. What evolved the Democrat Party was the Vietnam War and the hippie/druggie/treehugging/pro-commie movement. They *hated* Johnson and Humphrey.
But as the hippies grew up, dried out and got jobs (at least some of them) and the Democrat old guard died off, the hippies replaced them, learned networking and grew in power.
One thing is true about socialists - they see big government as their true god so they are relentless in pursuing it. They show up at the precincts. They volunteer, organize and evangelize.
They see the likes of Clinton as "one of them" and the true believers need no Kool-Aid. They've already bought into it all like a Scientologist dupe. They forgive the lies and half-truths of their leaders because the opposers to big government are their Satan. And any lie at any cost is worth defeating the non-believers.
I don't think the likes of Lyndon Johnson or even JFK would be happy with what the Democrats are today. They'd shake their heads and ask "what went wrong" just the way I imagine Martin Luther King would respond if he saw the Jesse Jacksons and Al Sharptons that have assumed his mantle.