I'd recommend Rick Perlstein's books. Reading Nixonland now and it's one of the best books I've read in a while, an absolute page-turner that traces the evolution of the American electorate through the 1960s, the Civil Rights Movement and Nixon's machinations that shifted the country so far to the right: the rise of dog-whistle politics, preying on racial fears, etc. (Compare post-Nixon to pre-Nixon politics). Also, the Democrats' loss of the South, as the other poster focuses on with The Rise of Southern Republicans.

Eager for The Invisible Bridge, the next book Perlstein wrote, about the transition from Nixon to Reagan as well. I'd recommend both, likely, but haven't finished Nixonland yet so I'd hold off on that.