THERE’S an old joke about two comedians sitting in a rowboat. One falls overboard. Not able to swim, he starts waving his arms and frantically screaming, “Hey! I’m dyin’ over here!” His friend calls back to him, “Go dirty!”

That sums up the presidential primary races this year, at least on the Republican side. And if you think there’s a lot of right-on-right nastiness, just wait until the general election campaign, when the raging right meets the livid left head-on in a country that is more politically polarized than it has been in many decades.

What can we do to improve the situation? Let’s start by considering what has happened. First, the average American is becoming more ideologically predictable. A Pew Research Center study from 2014 shows that the share of Americans with “consistently conservative” or “consistently liberal” views has more than doubled in the last two decades to 21 percent from 10 percent.

Second, despite the talk about divisions within the Democrats and Republicans, both parties are becoming purer ideological vessels, rather than mixed coalitions that cover broad spectra. In 1994, nearly 40 percent of Republicans were more liberal than the median Democrat, and 30 percent of Democrats were more conservative than the median Republican. Today, those numbers have plummeted to 8 percent and 6 percent.