In today's NYT Paul Krugman says the country is polarized because of growing inequality.

This is economic determinism 101.

Here's his thesis:

You see, the nastiness of modern American politics isn’t the result of a random outbreak of bad manners. It’s a symptom of deeper factors — mainly the growing polarization of our economy. And history says that we’ll see a return to bipartisanship only if and when that economic polarization is reversed.

After all, American politics has been nasty in the past. Before the New Deal, America was a nation with a vast gap between the rich and everyone else, and this gap was reflected in a sharp political divide. The Republican Party, in effect, represented the interests of the economic elite, and the Democratic Party, in an often confused way, represented the populist alternative.

In that divided political system, the Democrats probably came much closer to representing the interests of the typical American. But the G.O.P.’s advantage in money, and the superior organization that money bought, usually allowed it to dominate national politics. “I am not a member of any organized party,” Will Rogers said. “I am a Democrat.”

Then came the New Deal. I urge Mr. Obama — and everyone else who thinks that good will alone is enough to change the tone of our politics — to read the speeches of Franklin Delano Roosevelt, the quintessential example of a president who tackled big problems that demanded solutions.

For the fact is that F.D.R. faced fierce opposition as he created the institutions — Social Security, unemployment insurance, more progressive taxation and beyond — that helped alleviate inequality. And he didn’t shy away from confrontation.

“We had to struggle,” he declared in 1936, “with the old enemies of peace — business and financial monopoly, speculation, reckless banking, class antagonism, sectionalism, war profiteering. ... Never before in all our history have these forces been so united against one candidate as they stand today. They are unanimous in their hate for me — and I welcome their hatred.”

It was only after F.D.R. had created a more equal society, and the old class warriors of the G.O.P. were replaced by “modern Republicans” who accepted the New Deal, that bipartisanship began to prevail.

What's wrong with this thesis?

It doesn't get to the nitty gritty. We are polarized today because the postwar consensus has collapsed and nothing has taken its place. The consensus was held together in the 1930s by fear of depression and in the early postwar period by fears of communism. Once we put in place a safety net that protected Americans from the threat of economic disaster and Cold War tensions eased natural divisions in the society surfaced. Fear in effect had kept us united.

But fear only explains so much. To complicate the story even further: Periods of consensus occur when one party or the other dominates society so completely that almost no one dares challenge its hegemony. After the New Deal Republicans were so badly defeated that they shied away from confrontation for nearly half a century. Robert Taft tried to swim against the liberal tide; he drowned. Barry Goldwater tried; he also drowned. Not until the liberal consensus was undermined by both Vietnam and the race riots and the failures of the Great Society did Americans start to doubt the liberal assumptions they had shared since FDR. Liberal failures inspired a conservative resurgence.

Today the country is fairly evenly divided politically. Because both sides can taste power and neither is convinced their basic ideological approach is unpopular, they persist in battling for their ideas.

Don't like polarized politics? Too bad. They're here to stay until one side or the other achieves paramount political victory. This victory will have little to do with the size of the gap between the rich and the rest of us.