We have met the enemy and they are you

Since 1978, the American National Election Studies has asked people to rate the Democratic and Republican parties on a scale of 0-100 ("When I read the name of a group, we'd like you to rate it with what we call a feeling thermometer.  Ratings between 50 degrees-100 degrees mean that you feel favorably and warm toward the group; ratings between 0 and 50 degrees mean that you don't feel favorably towards the group and that you don't care too much for that group.  If you don't feel particularly warm or cold toward a group you would rate them at 50 degrees").  Here is a figure showing the percentage who give each party the lowest possible rating:

It has risen for both parties.  For example, in 1979, 1.7% of people rated the Democrats at zero and 4.2% rated the Republicans at zero; in 2016 the corresponding figures were 11.2% and 11.4%.  I also calculated the individual-level correlation between ratings of the Democratic and Republican parties--that is, the extent to which people who felt favorably towards one party felt unfavorably towards the other. 

The correlations are negative, so the downward slope means that the relationship is getting stronger.

You can combine the three measures (with a principal components analysis) to get a general measure of partisan polarization.

There is an upward trend, and it seems to have become stronger in the 21st century.  An interesting thing is that it doesn't track trust in government (discussed in this post) all that closely.  However, confidence in many institutions has followed a general downward trend (this post).   Of course, a lot of things have followed a trend since the 1970s, but it seems plausible in principle that polarization could cause or reflect declining confidence in institutions.