The uphill battle to confirm President Joe Biden’s pick to regulate the gun industry just got steeper.

Senator Pat Toomey announced on Thursday he would not vote to confirm David Chipman as director of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). The Pennsylvania Republican said Chipman’s support for strict new gun laws, including bans on popular firearms such as the AR-15, would be detrimental to his ability to run the agency.

“While I respect David Chipman’s nearly 25 years of experience as an ATF agent, I fear that his subsequent vocal support for policies that limit the rights of law-abiding gun owners and his past criticisms of those in the firearm industry would compromise his ability to carry out ATF’s mission effectively,” Toomey said in a statement. “As such, I am unable to support his nomination to lead the ATF.”

Toomey’s announcement, which comes less than a month after fellow centrist Republican Susan Collins (Maine) said she would vote no, makes it unlikely that Chipman will garner any Republican votes. Sources told The Reload on Tuesday that Senate Majority Leader Chuck Schumer (D., N.Y.) isn’t planning a vote on Chipman this week because he has yet to secure the 50 votes needed to confirm him. Without Toomey, who has voted to confirm several other Biden nominees, Schumer will have to rely entirely on a Democratic caucus that has at least four members still on the fence.

Chipman’s history of incendiary comments and his boosting of a Waco conspiracy theory have incited a great deal of controversy around his nomination. While Democrats like Senator Dick Durbin (D., Ill.) have argued the ATF needs a confirmed director after many years operating under various acting directors, critics have warned Chipman’s presence would damage the relationship between the agency and the industry it regulates. Chipman spent much of his confirmation hearing walking back mocking comments he made about new gun owners and assuring senators his personal support for implementing new gun bans and strict regulations would have no impact on how he runs the ATF.

But many senators remain skeptical about confirming a man on the payroll of Giffords, a major gun-control group, to lead the agency.

Senators Jon Tester (D., Mont.), Angus King (I., Maine), and Joe Manchin (D., W.Va.) have all publicly expressed doubt about Chipman this week, something Toomey also did Tuesday before he announced his decision. Ultimately, the Republican who campaigned alongside Manchin to pass a universal background check bill said Chipman’s history of gun-control activism is incompatible with a role that is meant to be nonpartisan.

“Meaningful progress on gun safety will only be possible when members of Congress and the executive branch drop the politics and hyperbole and focus on the possible,” Toomey said. “That likely will not happen if the ATF—the law enforcement agency tasked with enforcing the nation’s firearm laws—cannot be impartial in carrying out its duties.”