(FORTUNE Magazine) – Does this sound like an American political party you know?

It's become a congressional party, mildly interested in winning the presidency, but utterly devoted to consolidating power on Capitol Hill--where its members can control the budget process, call each other Mr. Chairman, and use Congress as a partisan battering ram against the White House. It's a divided party doomed to conduct its disputes on the ideological fringes, and one whose struggles serve only to move it further from the mainstream. Tiny fights over language, especially regarding abortion, take on enormous meaning. Its members see symbolism in the slightest gesture, betrayal in the mere discussion of compromise. It came to power talking the language of the people, but now seems to care more about what the think tanks think. And it is increasingly intent on using government as a tool of social engineering.

That used to be a good description of the Democrats. Now it describes the Republicans. In the marketplace of American politics, the two parties have just completed the Great Swap. Not that they've traded places consciously--or that they're even conscious of having done so. But the transformation helps explain the parties' behavior this winter, and it helps explain the way they're organizing themselves for battles yet to come.

At the heart of the transformation, as of so much else in Washington, are Bill Clinton and Newt Gingrich. It was Clinton who ended the Republicans' domination of the White House, who loped back to the center and dragged his party with him, who determined that, hard as it might be to live with an opposition Congress, it might be harder still to live with a friendly Congress. It was Gingrich who ended the Democrats' domination of Congress, who planted GOP lawmakers firmly on the right, and who calculated that the Republicans' drive toward majority status didn't necessarily require the White House.

So now the Democrats, whom you remember as the party of the special interests, are sitting back while the Republican special interests fight. Watch Gingrich and the House leadership bob and weave as the Christian right tries to assert its social agenda, especially on prayer in school and abortion, late this winter. Watch the big-business groups and others of the Old Republican Party struggle to retain their corporate welfare as the libertarians and the crusaders of the New Republican Party try to strip it away this spring.

Parties seek power to implement change, not realizing that power often changes the parties more than the broader society. Here's my law of political science: The bigger a party gets, and the more special interests it has, the more unavoidable are the disputes that imperil its unity. "If you're going to put together a coalition, you have to appeal to the sort of people who make your environment complicated," says George C. Edwards III, the director of the Center for Presidential Studies at Texas A&M University.

The Republicans--a party on the offense, but as l'affaire Gingrich made clear this winter, a party not ready for the fight--haven't reached a clearance in the political woods. They've merely swapped positions with the Democrats--a party on the defense that seems tired of the fight. In the two-step of American politics, they will almost certainly swap places again.

DAVID SHRIBMAN is Washington bureau chief of the Boston Globe and a Pulitzer Prize-winning political reporter.