A revealing anecdote during last fall’s remembrances of the Kennedy assassination described how Lyndon Johnson, the slain president’s successor, bullied Sen. Richard Russell of Georgia into serving on the Warren Commission to investigate the shooting.

Russell was a powerhouse conservative and segregationist. Johnson figured he’d balance the liberal commission chair, Supreme Court Chief Justice Earl Warren, maestro of a famously activist high court. Russell loathed Warren. Johnson didn’t care.

But here’s the historical oddity: Russell, the archconservative, was a Democrat. Warren, the liberal lion, was a Republican. Each belonged to a species that was common half a century ago but is now as extinct as the pterodactyl.

Consider three numbers from last week’s Star Tribune Minnesota Poll: 0, 1 and 3.

The poll found that only 3 percent of Minnesota Democrats disapprove of the job Mark Dayton is doing as governor. Just 1 percent of Democrats disapprove of Sen. Al Franken’s performance in office.

And Republicans? The poll reported 0 percent of them approving of President Obama’s handling of his job.

These are staggering levels of groupthink. And without making too much of any single poll result, a wealth of evidence confirms the basic message here. Our political parties have become pathologically pure, harboring, at least on certain questions, no more intellectual diversity than a beehive.

It’s almost unanimously agreed, of course, that America today is abnormally polarized, that we’ve seldom been so sharply divided. But is it possible that it’s only our political parties that are more estranged than they used to be?

Or, put another way, could today’s inflexible sorting of conservatives and progressives into rival partisan identities itself be the “problem” — the thing that’s rubbing political resentments raw?

Last week’s poll revealed various kinds of divides among Minnesotans — by geography, gender and age. But none compared with the partisan chasms. The most lopsided demographic leaning was young voters’ keenness for Franken. But their 73 percent approval looks like ambivalence beside Franken’s 97 percent endorsement from Democrats of all ages.

In 2012, the Pew Research Center for the People & the Press looked at polarization over time. It reported that it is only when they are sorted by party that Americans have grown more divided over the past quarter-century.

Averaged across 48 issues, the researchers said, “the average partisan gap … nearly doubled” from 1987 to 2012. But little or no widening showed up in the disagreements between black and white Americans; the more educated and less educated; the rich and the poor; the religious and unreligious, or males and females. Those groups differed, but only to the same extent as before.

It’s not news that our parties have undergone a rite of purification in recent decades. Traditionally, America’s parties were messy organic coalitions held together by geography, ethnicity, religion, economic interest, history and habit. The South stayed “solidly” attached to the Democrats for a century after the Civil War, even though on many issues it ceased to be a natural ideological fit. After bipartisan passage of the Civil Rights Act 50 years ago, the white South’s migration to the Republican Party did more than any other single development to turn each party into an echo chamber.

The mongrel parties of old were often unloved. Each contained both a conservative and a liberal wing, and philosophical battles raged as often within the parties as between them. But the parties’ organizational interest in holding their diverse coalitions together tended to soften rhetoric and increase flexibility. The problem, as many saw it, was that voters were given no sufficiently clear choice in the end.

George Wallace, another militant Dixiecrat of yesteryear, famously thundered that there was “not a dime’s worth of difference” between Democrats and Republicans. His gripe, put in more scholarly terms, was the basic theme of a landmark paper published in 1950 by the American Political Science Association, “Toward a More Responsible Two-Party System.” A long series of reforms since then, aimed at democratizing party processes and weakening party bosses, has also helped move the parties farther apart.

The Pew Center’s research director Scott Keeter said in a discussion of the 2012 study that “what many political scientists had been hoping for years ago … is coming true. The two parties are becoming more and more ideologically homogenous. But so far the result has been a dysfunctional political system that appears unable to govern …”

It may not be quite as bad as all that. With a few ugly compromises finally being worked out in Washington, perhaps we can hope our more polarized parties will yet learn to do business with each other. Or maybe Americans, now enjoying a “clear choice,” will eventually make one, giving one party or the other enough power to break through the gridlock.

In the meantime, it never hurts to be reminded to be careful what we wish for.


D.J. Tice is at Doug.Tice@startribune.com.