SYNOPSIS: Why has the Republican Party shifted to the right? Perhaps income inequality could provide some answers

When Congress returns to Washington, the battles will resume — and each party will accuse the other of partisanship. Why can't they just get along?

Because fundamental issues are at stake, and the parties are as far apart on those issues as they have ever been.

A recent article in Slate led me to Keith Poole and Howard Rosenthal, political scientists who use data on Congressional voting to create "maps" of politicians' ideological positions. They find that a representative's votes can be predicted quite accurately by his position in two dimensions, one corresponding to race issues, the other a left vs. right economic scale reflecting issues such as marginal tax rates and the generosity of benefits to the poor.

And they also find — not too surprisingly — that the center did not hold. Ralph Nader may sneer at "Republicrats," but Democrats and Republicans have diverged sharply since the 1980's, and are now further apart on economic issues than they have been since the early 20th century.

Whose position changed? Tom Daschle doesn't seem markedly more liberal than, say, the late Tip O'Neill. On the other hand, Tom DeLay, who will soon be House majority leader, is clearly to the right of previous Republican leaders. In short, casual observation suggests that American politics has become polarized because Republicans have shifted to the right, and Democrats haven't followed them. And sure enough, the Poole-Rosenthal numbers that show a divergence between the parties also show that this divergence reflects a Republican move toward more conservative economic policies, while Democrats have more or less stayed put. As people like James Jeffords and Lincoln Chafee have found, it has become very hard to be what we used to call a moderate Republican.

But why did the Republicans move to the right?

It could be a matter of sheer intellectual conviction. Republicans have realized that low taxes and small government are good for everyone, and Democrats just don't get it. But ideas tend to take root when the soil has been fertilized by social and economic trends. Dr. Poole suggests that the most likely source of political polarization is economic polarization: the sharply widening inequality of income and wealth.

I know from experience that even mentioning income distribution leads to angry accusations of "class warfare," but anyway here's what the (truly) nonpartisan Congressional Budget Office recently found: Adjusting for inflation, the income of families in the middle of the U.S. income distribution rose from $41,400 in 1979 to $45,100 in 1997, a 9 percent increase. Meanwhile the income of families in the top 1 percent rose from $420,200 to $1.016 million, a 140 percent increase. Or to put it another way, the income of families in the top 1 percent was 10 times that of typical families in 1979, and 23 times and rising in 1997.

It would be surprising indeed if this tectonic shift in the economic landscape weren't reflected in politics.

You might have expected the concentration of income at the top to provoke populist demands to soak the rich. But as I've said, both casual observation and the Poole-Rosenthal numbers tell us that the Democrats haven't moved left, the Republicans have moved right. Indeed, the Republicans have moved so far to the right that ordinary voters have trouble taking it in; as I pointed out in an earlier column, focus groups literally refused to believe accurate descriptions of the stimulus bill that House Republican leaders passed on a party-line vote back in October.

Why has the response to rising inequality been a drive to reduce taxes on the rich? Good question. It's not a simple matter of rich people voting themselves a better deal: there just aren't enough of them. To understand political trends in the United States we probably need to think about campaign finance, lobbying, and the general power of money to shape political debate.

In any case, the moral of this story is that the political struggles in Washington right now are not petty squabbles. The right is on the offensive; the left — occupying the position formerly known as the center — wants to hold the line. Many commentators still delude themselves with the comforting notion that all this partisanship is a temporary aberration. Sorry, guys: this is the way it's going to be, for the foreseeable future. Get used to it.

Originally published in The New York Times, 1.4.02