Chicago Mayor Rahm Emanuel, center, participates in a panel discussion on Reducing Violence and Strengthening Policy and Community Trust at the U.S. Conference of Mayors in Washington. (Gary Cameron/Reuters)

Chicago’s Rahm Emanuel loomed like a specter over a gathering of nearly 300 mayors in Washington on Wednesday.

At the U.S. Conference of Mayors, where Emanuel was scheduled to speak, TV crews roved through the lobby searching for the embattled Chicago mayor. One protester interrupted a morning news conference that Emanuel didn’t even attend by holding up a “#ResignRahm” sign, refusing to budge as the other mayors awkwardly tried to continue by talking around her.

For much of the afternoon, a scrum of reporters staked out the entrance to a panel discussion where Emanuel was supposed to speak. When it became apparent he wasn’t going to show, the other mayors on the panel proceeded without him — an empty seat in front with Emanuel’s name on it.

At a time when cities across the country are grappling with public outrage over police shootings in black neighborhoods, Emanuel has come to embody the thorny problems now facing all big-city mayors: how to restore public trust, how to reform police and how to handle exploding racial tensions. And, of course, how to do it all in the face of public anger and calls for your resignation.

Many mayors at Wednesday’s conference said they were just as eager as the TV crews to catch Emanuel and hear him speak. Some out of a morbid curiosity, like onlookers of a train crash, others in search of lessons on what went wrong and how to avoid ending up in similar hot water.

“As a mayor, we all know we could be facing that same situation at any moment,” said Eric Jackson, mayor of Trenton, N.J. “This is a guy who has been in the fire and has been dealing with all this, not as a hypothetical, but as a real crisis. There’s something to be gleaned from that.”

When Emanuel finally did materialize — for about an hour during lunch — it was on a panel about police reform and community trust. Emanuel shared the stage with Baltimore Mayor Stephanie Rawlings-Blake, who faced similar anger and calls for her resignation over charges of her city’s police brutality and how she handled protests and riots last year. Also on the panel was St. Louis Police Chief Sam Dotson, who had a close-up view of the 2014 protests over a police shooting in Ferguson, Mo.

For many, that panel — featuring officials involved in the ­nation’s three biggest crises over police shootings — provoked ­reflection as well as some degree of Monday-morning quarterbacking.

“It’s hard not to look at them and try to figure out what errors were made, what they look back in hindsight and regret,” said one East Coast mayor, speaking on the condition of anonymity to avoid publicly criticizing his colleagues.

“You want to say to Stephanie, ‘Why did you hold back when the protests were starting?’ ” said another mayor. “You want to ask Rahm, ‘What’s your real plan for tackling this problem?’ Because some of these new policies he’s announcing” — such as increasing the use of Tasers by police officers, he said — “we’ve been doing that for a while now.”

“I think the real question everyone here is trying to figure out is how to walk that line,” said Doug Palmer, former head of the Conference of Mayors and former Trenton mayor. “How do you say to the black community, ‘I hear your concerns,’ and at the same time tell the police, ‘I support you’ ”?

On the panel, Emanuel largely avoided addressing the ongoing anger in Chicago that has simmered since the release late last year of a video that showed a police officer shooting a black teenager, Laquan McDonald, 16 times.

He talked instead of the problem of gang violence, community-based policing, experiments with embedding federal officers in local precincts and the importance of education in addressing systemic issues in poor neighborhoods where many shootings take place.

“The trust factor is not just goal — it’s a key ingredient to effective community policing,” he said. “The public has to know there’s legitimate oversight, it’s certain and it’s not biased, and the truth is, we’re working at that — our city, other cities — because there’s a lot of judgment that the oversight has been lax and there’s not an accounting system.”

As the panel came to a close, Emanuel was spirited through a back door, to the disappointment of a sizable throng of reporters waiting in the wings.

In his absence, a few mayors traded predictions on whether Emanuel could escape the scandal with his reputation intact. “My take on it is, this guy just got reelected,” one mayor said in a hushed conversation. “He’s got three years to go, which is an eternity in politics. The Bears could win the Super Bowl. The Cubs could win a pennant. A lot could happen in the time he’s got left.”