As several moderate Senate Democrats gear up for potentially tough re-election fights in 2006, they are looking to lessons learned in 2002 and 2004 when deciding how much they should work with, and against, President Bush on his policy initiatives.

In the past four years, the Bush White House has deftly used its bully pulpit to define the Congressional mainstream, then drub even the most cooperative Democratic opponents if they fall short of full compliance.

Now, if anything, the challenge for Democratic moderates will grow even tougher, given the Republicans’ expanded Senate majority, several Senators acknowledged.

“It gives me the responsibility to define myself, and not let others define me,” said Sen. Ben Nelson (D-Neb.), who narrowly eked out a win in 2000 and is expected to face a stiff challenge from Republican Gov. Mike Johanns in 2006.

The Bush White House has become adept at knocking off centrist Democrats in moderate-to-conservative states, including former Sens. Max Cleland (Ga.) and Jean Carnahan (Mo.) in 2002 and Senate Minority Leader Tom Daschle (S.D.). The GOP also defeated a half-dozen attractive and moderate Democratic candidates in the South and other Republican-leaning states this year.

After Bush was inaugurated in 2001, many centrist Democrats — including Cleland, Carnahan, Sen. Mary Landrieu (La.), and Sen. Tim Johnson (S.D.) — decided to support many of the president’s initiatives as a way of protecting their right flank.

But simply voting for a $1.3 trillion tax cut and other lesser-noticed policies was not enough to win Democratic moderates a pass from this White House.

Rather, Bush campaign operatives went for the jugular by questioning the patriotism of Cleland, a triple amputee from his service in Vietnam, and by accusing others of unfairly obstructing the president’s initiatives. Only Landrieu and Johnson survived to serve another term — each narrowly.

Retiring moderate Sen. John Breaux (D-La.) said the White House has successfully upended moderate Democrats by employing a strategy he described as, “If you’re on the wrong side of guns, gays and God, then you’re not in the center.”

Democrats of all stripes have fought back by trying to turn those “morality” questions on their head by saying it is immoral to leave millions of Americans without health insurance and on the cusp of poverty. But Breaux noted that the White House consistently wins that argument in swing states because “those are not emotional issues.”

Breaux emphasized that moderate Democrats should remain “consistent with the people in your state. Then it doesn’t matter what [Republicans] do.”

Sen. Tom Carper (D-Del.), another centrist who’s up for re-election in 2006, said Democrats should continue to keep in close contact with centrist Republicans, so they can work together to define the parameters of the debate.

“Centrists Democrats, working with Republican centrists, have an equally good opportunity to define where the center is,” Carper said.

Carper also believes that many Republican moderates will feel freer than in the past to buck the White House and align themselves with like-minded Democrats, because the GOP doesn’t need to clamp down on internal dissension as much with Bush no longer on the ballot and with GOP majorities in both chambers assured for some time.

“My feeling is they might feel a little bit liberated,” said Carper. “In an odd way, it gives the Republican centrists a measure of independence and flexibility that they didn’t have over the past four years.”

Nelson agreed, saying, “The [Senate] Centrist Coalition will be defining bipartisanship as something more than the other side picking off the occasional Democrat.”

But most Democratic centrists pointed out that Democrats in general are less likely to oppose the president as vigorously as they did in the run-up to the 2004 election, having decided that their opposition contributed to their net four-seat loss in the Senate.

“There’s an argument going around among Democrats to just give him enough rope to hang himself,” said Sen. Max Baucus (D-Mont.), another centrist with a potentially bruising re-election contest in 2008. “After all, he’s got enough votes. There’s a real sense that since he won … you don’t want to oppose everything he wants.”

Carper agreed that giving Republicans the opportunity to alienate moderate voters by positioning themselves to the right “has a certain appeal to it.”

Still, that doesn’t mean centrists in both parties won’t be returning to their traditional role as dealmakers on everything from tort reform to a Social Security overhaul.

Carper said he sees the chance for Congress to reach agreement early in the next session on limiting the liability of asbestos makers while ensuring that people who are already sick from inhaling the deadly fibers are fairly compensated.

“A victory like that, early on, on a contentious issue … where our views have moderated the finished product will help set the tone for progress on other contentious issues,” Carper said.

Other Democrats up for re-election in 2006 who bill themselves as moderates are Sens. Bill Nelson (Fla.), Jeff Bingaman (N.M.). Maria Cantwell (Wash.) and Herb Kohl (Wis.). Nelson and Bingaman are running in states won by Bush in 2004.