LBJ: The Early Years is a solid work from director Peter Werner who's had a pretty long career on TV. For some reason, the screen writer of the mini-series isn't said anywhere, not in the credits nor in IMDb. I don't know why, certainly there's no reason for anyone to hide. LBJ: The Early Years starts from the fifties, with Johnson working in the senate, but not yet being a senator. The series follows his career in politics from running for senate and later for vice-presidency. The climax is of course the assassination of John F. Kennedy on which no time is wasted. The murder is not shown, the series focuses on the aftermath of the assassination. The series doesn't go into LBJ's actual presidency.
I'm no expert on the US history, but the mini-series seems trustworthy on many themes, like the relationship between the Kennedys and Johnson. As the series is not about LBJ's presidency, it doesn't deal with the war in Vietnam, so it can dust off the more difficult issues.
The best thing about LBJ: The Early Years is the lead actor. Randy Quaid makes a believable and likable Johnson, with all his quirks, Texas drawl and sudden changes in mood. Quaid is full of energy, when need be, but he's very good also portraying Johnson's depression. There are many good actors in the small roles: Kevin McCarthy, Pat Hingle, R. G. Armstrong, Barry Corbin, Royal Dano, Frances Conroy... In the narration are included several newsreels, which are used to a good effect.
I don't know if this is regularly shown on American TV, but it could very well be.
More Overlooked Films at Todd Mason's blog here (when they show up).