Democrats need their “Sister Souljah moment” with the outer left, and they need it now. The MoveOn.org ad — “General Petraeus or General Betray Us?” — was simply unacceptable. Not only was it dumb, but it created a distraction for Democrats trying to challenge Bush policy in Iraq.

“Sister Souljah moment” entered the political language in 1992, when presidential candidate Bill Clinton publicly rebuked black militant Sister Souljah over an outrageous remark. And he did it before a meeting of the Rainbow Coalition. Clinton took heat from Jesse Jackson and others, but he established his independence from radical elements within the Democratic Party.

MoveOn should be a positive force for Democrats. It raises lots of money and rallies disaffected liberals. But it has a history of dated tactics that — while gratifying to some on the fringes — alienates the moderate voters that Democrats need to win. Its messages too often make the left look juvenile.

In 2004, MoveOn ran a contest for anti-Bush ads and posted on its Web site a submission that likened the president to Adolf Hitler. MoveOn leaders recognized the mistake and urged colleagues to discourage commentary that Republicans could use to make them look like extremists.

But now, MoveOn has made a nasty personal attack on David Petraeus, and the general is not nearly the unpopular figure that Bush is.

“Simply put, the MoveOn people are a gift to the GOP,” Republican consultant Dan Hazelwood told Washington Post political blogger Chris Cillizza right after the ad came out. He is right.

Democrats showed great respect for Petraeus, even as they asked hard questions. But they had that silly ad hanging around their necks.

You can’t get more “antiwar” than Illinois Rep. Janice Schakowsky. But even she had to take time out to respond to reporters’ questions about the MoveOn ad, calling it “not an accurate statement.”

Delaware Sen. Joe Biden was on television calling Petraeus’ claims of progress “dead, flat wrong.” But he, too, had to interrupt his message to distance himself from the MoveOn statement. A Democratic candidate for president, Biden characterized the ad as “hard-edged” and Petraeus as misguided but “honorable.”

The American people already agree that the war was a dreadful mistake and badly run. The new Associated Press-Ipsos poll has 59 percent of respondents saying that history will judge the Iraq war as a failure, and only 34 percent as a success. This doesn’t mean that the public is in any mood for street theater directed against an admired general.

What is MoveOn.org up to here? Is this all about getting attention? If so, it’s succeeded.

Political activists on all sides have ravenous egos to feed, and the netroots of the left are no exception. They demand constant tributes from Democratic candidates — note the fawning performances at the last YearlyKos convention.

In reality, the hard left is not where the action is for the Democratic Party. It is in the purplish regions where moderates and independents decide outcomes. The party’s big victories in 2006 were in places like Missouri, Montana, Colorado and Virginia.

Rep. David Obey of Wisconsin had a near-Sister Souljah moment in March, when he argued that defeating the bill for funding the troops wouldn’t end the war but would deny the soldiers body armor and good military hospitals. “It’s time these idiot liberals understand that,” the Democrat said.

To make it a full-Sister Souljah moment, politicians have to say these things to their friends’ faces. Like Jackson in 1992, the targets of their censure will object, but they’ll get over it. Speaking real-world truths to their brethren on the left could spare Democrats much pain later on.

Froma Harrop is a Providence Journal columnist. Her e-mail address is fharrop@projo.com.