For starters, the two parties have become more ideological and more ideologically divided at the base. In a large survey of voters done in mid-1990, the Journal/NBC News poll found that just 12% of Republicans identified themselves as very conservative, and only 13% of Democrats identified themselves as very liberal. Today, those shares have roughly doubled. In the latest Journal/NBC News poll, taken last month, 28% of Republicans called themselves very conservative, and 26% of Democrats called themselves very liberal.

The share of blue-collar workers identifying themselves as Republicans has risen to 44% from 35%. Meanwhile, a somewhat higher share of Americans in the top income levels are likely to be Democrats than was the case 25 years ago.

And, amazing as it may seem now, a quarter century ago, those age 18 to 34 were more likely to identify themselves as Republicans than as Democrats; meanwhile, those age 65 and over were more likely to call themselves Democrats than Republicans. Today, the youngest Americans are far more likely to call themselves Democrats than Republicans, and the oldest Americans are as likely to call themselves Republicans as Democrats.

If you think about the logical implications of these shifts, today’s behavior makes more sense. A Republican Party that is more populist, conservative and Southern is likely to reject what such voters see as elitist establishment leaders and their moneyed interests. A Democratic Party that has grown younger and more liberal isn’t as likely to embrace a Hillary Clinton as it was her centrist, Southern governor husband, Bill. What seems crazy, in short, is in some ways perfectly logical.