Senator Jeff Flake (R-AZ) probably should have seen this coming when he decided to lie to the mother of a heroic mass-shooting victim.

Mayors Against Illegal Guns has released a new ad attacking Flake for his double-talk on expanding gun sale background checks. The spot features Caren Teves, whose son Alex was shot and killed shielding his fiancée during the Aurora, Colorado movie-theater shooting in July, 2012. Teves later wrote a letter to Senator Flake urging him to support a tougher gun laws, to which Flake replied “strengthening background checks is something we agree on.” Shortly thereafter, Flake voted against the Manchin-Toomey bill to expand background checks to cover all commercial gun sales.

Now Teves is calling the freshman senator out for his deception:

“The issue isn’t just background checks, it’s keeping your promise,” Teves says in the ad. “Senator Flake didn’t.”

After Flake voted against the Toomey-Manchin compromise, his approval rating plunged to an abysmal 32 percent, leading Public Policy Polling to declare him America’s least popular senator (for his part, Flake described his current standing among Arizonans as “somewhere just below pond scum”). The intense public pressure led Flake to publicly suggest that he could reconsider his opposition, although he has since shown no public signs of doing so.

The ad featuring Teves is one of three Mayors Against Illegal Guns spots criticizing Senator Flake. The other two can be seen below: