Currently reading Sen. Leahy's memoir. He entered the Senate in 1974 and was barely re-elected in 1980. It's an easy read, anecdotal and more about persons than policy or procedure.
One point--Reagan's victory in 1980 swept out a bunch of Democratic senators; only Leahy and Gary Hart of the 1974 Watergate class survived in the Senate. Was this the turning point to partisanship? He mentions Carter's farewell address, which included a warning against single-interest organizations. I think the reality is that organizations trying to influence Congress have become more and more specialized over the years. For example, we used to have the "farm lobby", composed of three big national organizations--Farm Bureau, Grange, National Farmers Union. But over time single commodity groups have become more important and more wide-spread.
I've got a couple books in my library queue about the growth of partisan politices; both of which I think go back to the 1990's, but not before.