Senator John Cornyn, a Republican from Texas, walked away from bipartisan talks to implement background checks for commercial gun sales on Wednesday.

Cornyn is a longtime ally of the gun lobby; his support for gun reform legislation may have signaled permission to Republican colleagues to get behind the effort. But his exit from the conversation is likely a death knell for a measure most Americans support. Democrats need at least 10 GOP votes in the Senate on any bill to overcome a filibuster.

Senator Chris Murphy (D-CT) has been leading the charge on background checks. “Getting John’s buy-in we thought was a way to get to 60,” Murphy said. Murphy added that he hasn’t given up hope and he’s still engaged in talks with Republicans including Sen. Lindsey Graham of South Carolina and Sen. Pat Toomey of Pennsylvania.

Murphy also said that Minority Leader Mitch McConnell’s (R-KY) opposition to gun reform has hindered the bipartisan effort.

“The fact that he’s not encouraging any of these discussions isn’t helpful,” Murphy said. “It’s no secret he’s never been interested in getting a background checks bill done, it’s no secret he’s never been interested in getting an infrastructure bill done.”

Senate Majority Leader Chuck Schumer has promised to bring up background checks legislation for a vote before a week-long July 4 recess.