[F]or the past century, political polarization and economic inequality have moved hand in hand. Politics during the Gilded Age, an era of huge income gaps, was a nasty business — as nasty as it is today. The era of bipartisanship, which lasted for roughly a generation after World War II, corresponded to the high tide of America's middle class. That high tide began receding in the late 1970's, as middle-class incomes grew slowly at best while incomes at the top soared; and as income gaps widened, a deep partisan divide re-emerged.

Both the decline of partisanship after World War II and its return in recent decades mainly reflected the changing position of the Republican Party on economic issues.

Before the 1940's, the Republican Party relied financially on the support of a wealthy elite, and most Republican politicians firmly defended that elite's privileges. But the rich became a lot poorer during and after World War II, while the middle class prospered. And many Republicans accommodated themselves to the new situation, accepting the legitimacy and desirability of institutions that helped limit economic inequality, such as a strongly progressive tax system. (The top rate during the Eisenhower years was 91 percent.)

When the elite once again pulled away from the middle class, however, Republicans turned their back on the legacy of Dwight Eisenhower and returned to a focus on the interests of the wealthy. Tax cuts at the top — including repeal of the estate tax — became the party's highest priority.

But if the real source of today's bitter partisanship is a Republican move to the right on economic issues, why have the last three elections been dominated by talk of terrorism, with a bit of religion on the side? Because a party whose economic policies favor a narrow elite needs to focus the public's attention elsewhere. And there's no better way to do that than accusing the other party of being unpatriotic and godless.

Thus in 2004, President Bush basically ran as America's defender against gay married terrorists. He waited until after the election to reveal that what he really wanted to do was privatize Social Security.

Pre-New Deal G.O.P. operatives followed the same strategy. Republican politicians won elections by "waving the bloody shirt" — invoking the memory of the Civil War — long after the G.O.P. had ceased to be the party of Lincoln and become the party of robber barons instead. Al Smith, the 1928 Democratic presidential candidate, was defeated in part by a smear campaign — burning crosses and all — that exploited the heartland's prejudice against Catholics.

So what should we do about all this? I won't offer the Democrats advice right now, except to say that tough talk on national security and affirmations of personal faith won't help: the other side will smear you anyway.

But I would like to offer some advice to my fellow pundits: face reality. There are some commentators who long for the bipartisan days of yore, and flock eagerly to any politician who looks "centrist." But there isn't any center in modern American politics. And the center won't return until we have a new New Deal, and rebuild our middle class.

I don't say this nearly often enough: what a pleasure -- a life saver, really -- it is to have Krugman out there. At least, at the very least, we know that there is one rational and intelligent voice speaking up in the mainstream media for seeing the nature of social, political and economic reality as it actually exists.

We should expect the Rovian swift-boating, anti-gay marriage, anti-terrorist, anti-illegal alien playbook to be in full force again this election, since there's nothing else the Republicans can conceivably run on, such as accomplishments, ability, integrity or honor.

[Thanks to Cathie]