I came of political age in the '70s, watched Watergate unfold, can still remember where I was when we learned Nixon resigned; the Left's hatred of him was implacable, I've read that was true since around 1948-50. But things weren't quite so bad after he left the scene. We loathed Slick Willie with a passion (now, not so much...), but we could at times work with him.
The 2000 election, though, that really polarized things, protesting the legitimacy of an election at the highest levels is utterly dangerous (one of the greatest things about our sorts of systems is solving the succession problem, one set of people running the nation replacing another), and Obama hasn't helped.
Although you do have a point about how the MSM treats budget conflicts for a Democratic vs. a Republican Congress. One complicating factor is that the Republicans did not control both houses during the period 1955-1993.
The difference today is other people have audiences. So, instead of becoming the bastions of accuracy and fact checking, the NY Times, ABC, NBC, etc. have continued to be pundits. Washington hasn't changed one bit since the 1800 election, its the fourth estate that tries to influence instead of inform.
Before, when people didn’t have access the way they do now, the small connected elite of politicians and other decisionmakers were able to coerce and smooth out issues for their constituency. Now, for better or worse, the people’s views are being enforced more directly.
As for "access", one counter WRT to this study's claimed time frame is the end of the "Fairness Doctrine", which severely stifled radio and TV political discussion from not all that long after its promulgation in 1949 until its end in 1987 (https://en.wikipedia.org/wiki/Fairness_Doctrine). Conservative talk radio, Rush Limbaugh being the best known example, became a major thing immediately afterwards. That channel, outside the control of the "small connected elite" became a driver of politics well before 1996.