Unless they can’t help themselves, it strikes me as political madness for Democrats to declare that the Iraq war is an “intractable quagmire” or a “grotesque mistake.”

If the war turns out to be a disaster — and let’s pray it doesn’t — then voters will repudiate Republican foreign policy in 2006 and 2008, and Democrats will be the beneficiaries.

So why should some Democrats now be acting as though they want to see their country lose a war? Why should they say things that may undermine the morale of U.S. forces and our Iraqi allies and contribute to a U.S. defeat?

[IMGCAP(1)]And why should they reinforce the image of their party as being so hopelessly force-averse that it can’t be trusted to lead on foreign policy?

It’s one thing for a Democrat like Sen. Joseph Biden (Del.) to harshly criticize the way the Bush administration is conducting the war and then recommend constructive steps for winning it.

Arguably, Sen. Carl Levin (D-Mich.) is doing something similar in calling for U.S. threats designed to keep the Iraqi government’s constitution-writing process on schedule, although he’s not exactly demonstrating support for allies who are risking assassination every day.

But what Sen. Edward Kennedy (D-Mass.) and House Minority Leader Nancy Pelosi (D-Calif.) have done with their “quagmire” and “grotesque mistake” talk is to declare that the war is, in effect, a lost cause.

The closest Kennedy comes to a positive suggestion is to call for Defense Secretary Donald Rumsfeld to resign. Then what? Pelosi and Senate Minority Leader Harry Reid (D-Nev.) are demanding that President Bush come up with a new strategy, but they are offering none of their own.

Democrats of all stripes go out of their way to declare that they support U.S. troops, but Kennedy and Pelosi are implying that those men and women are fighting and dying in vain.

The logic of the Kennedy-Pelosi position should lead them to call for immediate withdrawal, but they aren’t doing that either.

To be sure, they aren’t alone in defeatism. Democrats are gleefully quoting Republican Sen. Chuck Hagel (Neb.), who says that “the reality is that we’re losing in Iraq.” Hagel, though, is virtually the only public Republican naysayer, while it’s hard to find a Democrat who supports the war.

There are three explanations, not mutually exclusive, for what Democrats are doing in stepping up attacks on Bush’s Iraq policy now.

One is that they are taking advantage of polls showing that the public has turned sharply negative on the war. Another is that they want to claim vindication amid rising casualty rates. And a third is that they just want to keep saying what they think — that the war is a loser.

The polls have indeed gone south on Bush. The latest Gallup poll shows that support for the war has dropped to just 39 percent, down from 72 percent in April 2003 and 47 percent this March. Fifty-nine percent oppose the war.

At last week’s hearing of the Senate Armed Services Committee, Republican Sen. Lindsey Graham (S.C.) said with some alarm that support is flagging even in South Carolina — “the most patriotic state I can imagine.”

He added, “I don’t think it’s a blip on the radar screen. I think we have a chronic problem on our hands” that could lead to a premature U.S. withdrawal and an insurgent victory.

Rumsfeld gave Graham a good answer: This is “the time that leadership has to stand up and tell the truth. If you’re facing a head wind, you’ve got two choices. You can turn around and go downwind or you can stand there and go into the wind, and that’s what needs to be done.”

Clearly, that’s what the Bush administration is doing. Secretary of State Condoleezza Rice said the Bush policy is to keep U.S. troops in Iraq “as long as they are necessary,” although Democrats have been calling for an “exit strategy.”

The danger is that defeatism at home will create a defeatist dynamic in Iraq. As Gen. John Abizaid, commander of U.S. forces in the Persian Gulf, told the committee that among “our troops and the troops we’re training in the Iraqi and Afghan security forces, I never sensed the level of their confidence higher.”

“And when I look back here at what I see is happening in Washington, within the Beltway, I’ve never seen the lack of confidence greater.”

He added that, “when my soldiers … ask me the question whether or not they’ve got the support from the American people, that worries me. And they’re starting to do that.

“And when the people that we’re training, Iraqis and Afghans, start asking me whether we have the staying power to stick with them, that worries me, too.”

Herein lies the danger that Iraq could be Vietnam all over again.

A thick book came out this spring, “Vietnam Chronicles: the Abrams Tapes,” recounting the dismay of U.S. commander Gen. Creighton Abrams as his and South Vietnamese forces won battle after battle against Communist troops from 1968 to 1972, but lost the war on the home front.

After the 1968 Tet offensive — an allied military victory, but a psychological defeat —the media and the Democratic Congress decided that the war was “unwinnable” and it gradually became so.

Abrams complained that it was impossible to get beyond “the umpires” — the media bureau chiefs in Saigon and the Congress — who wouldn’t listen to reports of military progress.

“Whenever this command goes out to explain how it did something well, they’re calling you out before the throw is made to the plate. That’s the game we’re in.”

Obviously, it’s up to President Bush to run the war well and to rebuild domestic support for his policies. He has some progress to show: increasing numbers of Iraqis trained, a constitutional process under way, the decision of some Sunnis to take part in politics, aggressive new action against the enemy.

Bush’s policies may fail on their own because they were misconceived or badly executed. What shouldn’t happen is for U.S. policy to fail because Americans lose their will. Bush’s critics, the Democrats, should tell him how to win, not declare that the cause is lost.