Gun control advocates say the National Rifle Association-aided recall of two Colorado legislators who backed new gun restrictions will make it harder to revive stalled efforts in Congress to tighten firearm laws.

Federal legislation expanding background check requirements for gun buyers fell five votes short in the Senate in April, despite political momentum from last December’s massacre at a Connecticut elementary school. Gun control backers say they have yet to win a single new Senate supporter, and many worry that the muscle shown by pro-gun groups and voters last week in Colorado will make it even harder to find converts.

“The NRA does its job better than our side does our job,” said Jim Kessler, a co-founder of Third Way, which advocates for centrist Democratic policies. “They know how to influence and intimidate elected people.”