The extent to which the electorate has become more polarized over time is rather controversial, with Morris Fiorina leading the charge for the side that says it's pretty much the same-old-same-old. Party and ideology are, after all, different, and there isn't much sign of the electorate growing that much more ideologically coherent. For the Fiorina take, try Culture War? The Myth of a Polarized America.
I tend to come down on Fiorina's side. Except that negative partisanship is kind of real. Abramowitz and Webster focused on public opinion, but Congress has also seen similar patterns. Congress-watchers have noted that Congress itself has seen a breakdown of cross-party relations. One of the observations I have made on occasion here is about Orrin Hatch. He's retiring now, but he managed to hang on a little longer than he otherwise would by turning into more of a partisan warrior than he used to be. He was always a conservative, but party and ideology aren't the same. You can be a conservative without being an asshole to Democrats. That's how Hatch was, once upon a time. He was friends with Ted Kennedy! He bragged about it. Now, noooooobody brags like Trump, but Hatch was pretty good at bragging about his friendship with Ted Kennedy, and that was part of his thing. See? I'm conservative, but I work with Democrats! Aren't I awesome? Also, I'm a professional songwriter! (Um... uh... kind of...)
Then, Utah had its 2010 mess. Utah's nominating system is weird. In order to get on the primary ballot, Utah's other GOP Senator, Bob Bennett, had to have his name placed there by a nominating convention. Bennett, though, was a lot like Hatch, and 2010 was the year of the tea party. Bennett had been working with a Democrat-- Ron Wyden-- on a healthcare bill, so the GOP yanked his name from the primary ballot.
And Hatch turned into a partisan warrior, out of fear that the same might happen to him if he didn't. He was up in 2012, and he had no such problems.
Cross-the-aisle friendships in Congress are gone. A lot of that is ideological polarization. It is hard to be friends with someone who disagrees with you on everything, but possible. It's harder when their job is to work at cross-purposes with you. Then again, Orrin Hatch and Ted Kennedy were friends. Hatch turned into a pure partisan warrior only after Kennedy died, it is worth keeping in mind...
Animosity in Congress is about as bad as we have seen in the modern era (because, yeah, duels 'n stuff...). Now, they aren't pulling guns on each other... yet, but according to Politico's interview with John Boehner, Don Young pulled a 10-inch knife on Boehner, and that was within their party!
So, what does defective-Tom Cotton's memo have to do with this? Well, a) it's total fucking bullshit, b) it's the use of a congressional committee for pure partisan warfare, and c) it consequently exacerbates negative partisanship in Congress. That's real too. Abramowitz and Webster weren't focused on it, but despite the fact that scholars get an automatic exemption on human subjects research for interviewing Members of Congress, they are, technically speaking, human.
Bipartisanship cannot happen in Congress on anything substantive. Period. Note that not all policy matters are ideological! Note, too, that ideology changes over time! Race, for example, used to be a very different kind of issue, in partisan terms. Even beyond that, trade is a weird one. What is the liberal or conservative position on TPP? Start talking trade and you'll notice that Bernie Sanders and Donald Trump sound equally stupid. (Why? They are both morons who don't understand economics!) Not everything is left-right ideology. In legislative studies, we rely heavily on Keith Poole and Howard Rosenthal's NOMINATE scores to explain roll call voting, and you can explain over 90% of roll call votes with one dimension (liberalism/conservatism), but that's not 100%. There's more goin' on there, but as long as you have partisan animosity overshadowing everything, nothing can happen.
So, when Existential Philosopher, Devin Nunes comes along with his "memo" of weapons-grade bullshit, constructed to defend Trump from anything that Mueller finds with nonsense distractions, what does this do to the prospect of any bipartisan work on those few issues that might not be ideological?
Infrastructure? Rail improvements, maybe?
How much of an effect will Nunes really have on this? How much worse could it really get?
As I wrote earlier, whenever you think we've hit rock-bottom, don't worry. We're about to get dragged down through the fucking rock.