The six-person Democratic primary election for mayor is now just eight days away. The endorsement lines are drawn.

Candidate A got the nod from this labor union and that progressive group. Candidate B is backed by these elected officials and that clergy group.

Candidates C, D, E, and F are endorsed by - well, we're probably past the point where that matters.

The race breaks down to a final sprint between former City Councilman James F. Kenney and State Sen. Anthony Hardy Williams.

Kenney has the lead, according to pro-Kenney polls. Williams, if he has any polls showing him good news, isn't sharing.

So endorsements matter. But this election season also features a more curious form of support.

Call it the shadow endorsement.

It's coming in different ways in the closing days ahead of the May 19 primary from some of the most politically powerful men in Philadelphia - Mayor Nutter, City Council President Darrell L. Clarke, and former Gov. Ed Rendell.

Consider Nutter last week so very publicly slapping down Williams' suggestion that Police Commissioner Charles H. Ramsey must be rushed out of the Roundhouse for employing stop-and-frisk tactics he was hired to use.

Nutter's hit on Williams - questioning whether he is smart enough to be mayor - helped Kenney maintain a sense of momentum as the front-runner.

Williams' going after Ramsey is understandable. He wants to harness for his campaign the energy that has buzzed across big and small cities nationwide in recent weeks, building from long-held tensions between police and people of color.

That's why he turned up at the April 30 "Philly is Baltimore" march, where protesters drew attention to the violent death of a young black man in the custody of that city's police department.

Two days later, Clarke and Kenney spent a Saturday walking the streets of predominantly black North Philadelphia. He introduced Kenney to residents and community leaders as a friend for two decades.

Clarke didn't call the walk an endorsement. He didn't have to. The shadow was there for all to see.

Williams has also taken some heat for the race's lone all-negative ad, a 30-second television spot dredging up comments Kenney made in 1997 about restrictions on the use of force by police officers.

Rendell last week called the ad "factual but unfair" because Kenney's comments were 18 years old.

Rendell knows a thing or two about negative ads.

He ran an ad filled with fire and smoke in his 1987 bid to defeat Mayor W. Wilson Goode Sr. The ad focused on the city's 1985 decision to drop a bomb during the MOVE confrontation, a choice that cost the lives of six adults and five children and scarred Goode's political record.

Rendell lost that race but became mayor four years later. He served eight years and still had enough juice that his 1999 endorsement of former City Council President John F. Street had impact.

Street wasn't so lucky. His administration ended under the cloud of a federal investigation. His endorsement was not exactly a valuable commodity, though Nutter did manage to exploit Street's record for his campaign.

Nutter last week said he didn't "have any plans at this moment" to endorse a candidate for mayor.

His defense of Ramsey is part of a larger effort he started in January, assembling reports and statistics and polling, to show what he has accomplished.

Any defense by Nutter that depicts Williams as the bad guy inevitably paints Kenney as the hero.

That may be by design, or simply how the shadow falls.