Professors Marc Hetherington and Thomas Rudolph cited a 2011 poll that "asked people to place the Republican Party and the Democratic Party on a feeling thermometer that runs from 0 (really hate the group) to 100 (really love the group). The average score Republicans gave the Democratic Party was just 18 degrees, and the average score Democrats gave the Republican Party was the same, 18 degrees. When Jimmy Carter was president, those average scores for the other party tended to be in the mid-40s. Even as recently as Bill Clinton’s presidency, they were always at least solidly in the upper 30s. To understand the depth of the recent upturn in negative feelings, we should recall that the late Clinton-era readings were taken even as one party was impeaching the president of the other party."
It seems an important indication of how politics is today that partisans express more negative feelings toward the other party than they do toward atheists. It is not just lower scores on feeling thermometers, either. Shanto Iyengar and his co-authors find, among other things, that partisans are increasingly uncomfortable with their children marrying people who identify with the other party.I've argued that another contributing factor to our hyperpartisanship is that each of the past 3 presidents have been viewed as fundamentally illegitimate by a large segment of the opposition party.
Whatever the sources of the anger and mistrust, the result is a toxic and dysfunctional political system.