I have long loved Robert Caro's books, beginning with The Power Broker (and I recommend getting a hard bound copy, possibly secondhand: it's a big book and a good binding helps.

I particularly want to recommend The Path to Power, the first vojume of his LBJ books. The section on bringing electricity to the rural hill country is moving, epic poetry. His wife contributed significantly to the research on that section, and it is something I can read again and again. (And again, a secondhand hardcover edition in good shape is an excellent choice.)