Late last year, New York City Mayor and billionaire Michael Bloomberg launched a super PAC to counter the National Rifle Association when it comes to elections. Since new gun control measures failed in the Senate in April, Bloomberg has been out for blood running ads against Democrats who didn’t vote for those measures. But it turns out, Bloomberg’s efforts to unseat anti-gun control Democrats are backfiring.

Of the 35 Senate seats up for grabs in 2014, the 10 most contested battles come in mostly rural, conservative-leaning states such as Montana, West Virginia, Alaska and Arkansas, and nine of them are held by Democrats. Every Republican up for reelection in 2014, including the top GOP leaders, Sens. Mitch McConnell (Ky.) and John Cornyn (Tex.), have demonstrated that their biggest political fear is a primary challenge from the right, making them much more receptive to supporting the NRA’s position.

With parents of the young Newtown victims providing emotional reminders of the shooting for lawmakers Wednesday, one of their most high-profile political allies, New York Mayor Michael R. Bloomberg (I), adopted sharper tactics, urging thousands of his city’s top political donors to withhold donations from four Senate Democrats who voted against the gun bill.

In a letter to more than 1,000 donors, Bloomberg called out the four Democrats — Sens. Max Baucus (Mont.), Mark Begich (Alaska), Heidi Heitkamp (N.D.) and Mark Pryor (Ark.). “Instead of rising above politics to pass a law that would save lives,” he wrote, the four senators “sided with a gun lobby increasingly out of touch with Americans’ priorities.”

“The next time these four Senators want you to support them with donations to their campaigns, tell them you cannot,” Bloomberg wrote.

By asking campaign donors to withhold funds, the deep-pocketed mayor went against the will of his congressional Democratic allies, who tried but failed to secure enough GOP support for the gun bill and have warned that public criticism of vulnerable Democrats who voted against the bill will result in Republican gains and less of a chance to enact new gun laws.

Since the bill’s defeat in April, Bloomberg’s anti-gun group, Mayors Against Illegal Guns, has spent hundreds of thousands of dollars targeting senators of both parties for voting against the measure. A group founded by former congresswoman Gabrielle Giffords (D-Ariz.) — who was severely wounded in a January 2011 shooting — also has raised millions of dollars as it airs radio and television ads.

And the punch to the gut comes from fellow New Yorker Chuck Schumer.

Speaking to Time magazine, Schumer suggests Bloomberg’s targeting of pro-gun Democrats for their votes against gun-control legislation is unproductive.

“Frankly, I don’t think Bloomberg’s ads are effective,” Schumer said. “The Mayor of New York City putting ads against people in red states is not going to be effective.”

There’s a reason Obama didn’t run on gun control in 2008 or 2012. It’s a losing issue especially for Democrats in red states, something Bloomberg is learning the hard way.