WASHINGTON – After a dominating political victory, as in 2008, the expectations of a party’s most ideological elements are raised. With sufficient boldness, and sufficient ruthlessness, anything seems possible.

But the American two-party system has a self-correcting mechanism that is Madisonian in its balance and elegance. A party becomes more dominant by becoming more diverse. Losing parties shrink toward their ideological core, as Republicans have done. Winning parties expand to encompass more of the ideological center, the undeniable Obama achievement. But this places centrists in positions of legislative influence, which enrages activists who feel the moment for ambition has finally arrived.

Thus the current health care debate taking place largely within Democratic ranks.

Democrats begin as the more diverse of the two main political parties. About 38 percent of Democrats consider themselves liberal, 40 percent moderate and 22 percent conservative. By way of contrast, 73 percent of Republicans describe themselves as conservative. A Democratic majority is already a coalition. And recently added Democratic legislators have tended to win in purplish portions of the country.

It is among moderate and conservative Democrats, along with independents, that concerns about spending and the deficit are rising sharply. In March, Democrats of every ideological brand overwhelmingly believed more spending was essential to improve the economy. Now 48 percent of moderate and conservative Democrats put a greater priority on cutting spending to lower the deficit – a view shared by 56 percent of independents.

So how are these moderate elements being treated by the Democratic establishment? For the most part, with contempt. Liberal interest groups, and even the Democratic National Committee, are running ads targeting Democrats with moderate views on health reform. It is the Chicago-style, political hardball that some political operatives imagine is sophisticated but is often counterproductive. Do Sens. Evan Bayh, Mary Landrieu and Ben Nelson really need to be lectured by the left of their party on the interests and views of their own constituents?

And Majority Leader Harry Reid’s threatened use of reconciliation to pass health reform – a procedural maneuver allowing parts of the bill to pass the Senate by a simple majority instead of 60 votes – is a direct assault on moderates. This legislative “nuclear option” is not aimed at conservatives, but at centrists, who are likely to be found in the margin of 10.

The White House and congressional leaders are increasingly conveying a desperate message: Pass health reform quickly, before the congressional recess, before the great moment is lost. In other words, before details of the plan are examined too closely, before concerns about spending and the deficit take even broader hold.

But it may already be too late for that. President Barack Obama remains a skilled and popular leader. But with his approval in the 50s and slipping among independents, he now seems more like a political mortal (his approval rating, in a recent poll, ranked 10th among the dozen post-World War II presidents at this point in their tenures). The Pelosi stimulus package not only has had minimal economic effect; it has increased public skepticism that Congress is capable of spending such vast sums wisely. Trillions of dollars in stimulus and bailouts, resulting in record levels of predicted debt, have made the addition of a trillion-dollar health entitlement seem ill timed, even to supporters of expanded coverage. And in a continuing recession with rising unemployment, the imposition of massive new taxes to fund health reform would be reckless – adding burdens to a pack mule already on its knees.

It is difficult to imagine that an overwhelmingly Democratic Congress will do nothing on health reform. But as deadlines slip, and moderate arguments gain in momentum, the legislation is likely to disappoint liberal Democrats in several ways. William Galston of the Brookings Institution – who kept an eye on moderate congressional opinion as part of the Clinton White House – predicts that centrists “are not going along with a bill that isn’t genuinely revenue neutral, without tricks.” Taxes will need to be “sensible,” which “takes the House approach (boosting taxes on the rich) off the table.” Moderates, he says, “won’t support a version of the public option that weakens or eviscerates the private sector in the provision of health insurance.” And “there is broad agreement that any bill that is 90 percent expanded coverage and 10 percent cost control would be a disaster in the long run.”

Some may accuse such moderates of lacking in boldness or ambition. It is better than lacking in responsibility and good judgment.

© 2009, Washington Post Writers Group