WASHINGTON — Mayor Bloomberg’s anti-gun club suddenly isn’t such a hot ticket.

His gun-control group Mayors Against Illegal Guns has lost more than 50 of its original mayoral members in the last few months, as disenchanted mayors quit the coalition or leave office.

Bloomberg, who pumped millions of dollars of his personal fortune into the group to make it one of the loudest voices in the gun-control debate, now is struggling to replace ex-members.

“The original focus, I thought, was going to be . . . on better enforcement of our existing laws, and if anything, we have talked about not getting involved with things like banning assault weapons and banning magazine clips,” former member Rockford (Ill.) Mayor Lawrence Morrissey told BuzzFeed, which first reported the dwindling membership.

Morrissey received rousing applause at a town hall meeting last month when he announced he was quitting Bloomberg’s group.

“The reason why I joined the group in the first place is because I took the name for what it said — against ‘illegal’ guns,” he told the crowd.

Mayors Against Illegal Guns has focused almost exclusively on banning weapons and other tough new gun-control measures.

The group’s tactics also has ruffled feathers across the political spectrum:

* Top Democrats balked when Bloomberg’s group mounted a TV ad campaign targeting vulnerable Senate Democrats in red states who didn’t back a bill to expand background checks, potentially helping Republican challengers.

Sen. Charles Schumer (D-NY) slammed the move, saying the “mayor of New York City putting ads against people in red states is not going to be effective.”

* Victims-rights advocates blasted Mayors Against Illegal Guns for promoting a list of gun-violence victims that included the name of accused Boston Marathon bomber Tamerlan Tsarnaev and at least 10 wanted murder suspects. The group later apologized.

* Government watchdogs were up in arms when Bloomberg used city government Internet servers to host the group’s Web site.

* A Colorado gun-rights organization last week staged a “counter-rally” when Mayors Against Illegal Guns held an event in Aurora, Colo., to mark the first anniversary of the movie theater massacre.

Nashua (NH) Mayor Donnalee Lozeau quit Bloomberg’s gun-control team after it launched TV attacks against GOP rising star Sen. Kelly Ayotte of New Hampshire.

“I said, ‘Wait a minute, I don’t want to be part of something like that,’ ” Lozeau told the Manchester (NH) Union Leader. “I told them, ‘You’re Mayors Against Illegal Guns, you’re not mayors for gun control.’ ”

City Hall disputed claims that it is losing members.

“We now have more than 1,000 mayors in the coalition nationwide, compared to 650 last year,” said Bloomberg spokesman John McCarthy.

Mark Glaze, the director of Mayors Against Illegal Guns, said the turnover of mayors causes fluctuations in membership.

“Mayors come and go,” he said. “We lose them on occasion, but it’s going upward.”