Basically, during the middle of the twentieth century, the Democratic Party was internally incoherent, largely because civil rights legislation split the party into two distinct regional wings. (A chart focused on where the parties stand on civil rights shows even greater discrepancies, with southern Democrats by far the most conservative group.) This divide created an imperative toward bipartisanship whose implications have been described many times, including by Poole in a 2005 essay (PDF):
In Congress all three parties easily formed coalitions with one of the others against the third depending on the issue at hand. The northern and southern Democrats united to organize the House and Senate and thereby seize the spoils due the “majority” party. The northern Democrats and Republicans united to pass the 1964 Civil Rights Act and the 1965 Voting Rights Act, and the “conservative coalition” of Republicans and southern Democrats united to block liberal economic (and in the 1970s, social) policies.
What happened after the major victories on civil rights legislation in the 1960s is that civil rights stopped existing as a separate political debate; instead, racial issues were absorbed into the long-running debate over regulation and redistribution that forms the core divide in American politics. And conservative southern Democrats—the bloc whose existence had made bipartisanship possible, and even necessary—started to disappear.
There’s more to the story. The bipartisan era featured different issue divides and what was, in effect, a third party. But it also featured another factor that made legislating more complex, and cross-cutting alliances more viable, than they are today—much weaker party leadership, and many more power centers within Congress. As the parties became more ideologically coherent, institutional changes gave more power to party leaders. And they exercised that power by creating incentives for party loyalty (and punishments for its absence), and by structuring the agenda accordingly.
Another researcher, Sean Theriault, has documented how procedural votes—which tend to produce more polarized outcomes than substantive votes—account for an increasing share of congressional activity, as anyone who followed the health care debate can attest. Changes to the structure of roll call votes, and the issues decided by those votes, “over the last 30 years, account for roughly half of the polarization in Congress,” Theriault found (PDF). (In the same event at which Lott made his remarks, former House Speaker Tom Foley actually spoke about the role of party leaders in driving polarization. His comments merited two paragraphs in the McClatchy story, about three-quarters of the way through.)
Does all this make Lott wrong, or mean that Seidman is wrong to treat him as an authority on this subject? Not entirely. Of course there’s a personal element to legislating. Of course people who enjoy each other’s company, and who develop some level of mutual trust, will find it easier to work together. And of course Lott is a credible figure on how social mores in Congress have changed since his career began.
But on the much, much more interesting questions—how much of the rise in partisanship do those changing mores explain, and what else might explain them?—Lott really isn’t an authority at all. Treating him as one is sort of like treating a pitcher as an expert on the physics behind a curveball—you might get something interesting out of the conversation, but if you really want an informed perspective, you’re better off asking someone who’s actually studied the issue at hand.