A nominee to lead a federal gun regulation and enforcement bureau drew criticism Wednesday from Republicans on the Senate Judiciary Committee for his previous advocacy for gun control actions such as banning assault-style rifles.

David Chipman told senators that he took one position as an advocate on potential gun control laws, but would only enforce the current laws as director of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

For example, under questioning from Texas Republican Sen. Ted Cruz on whether he wanted to ban AR-15-style guns, Chipman said his view as an advocate would be to ban their manufacture and sale and also use an existing law to regulate those already owned by Americans.

“As ATF director, if confirmed, I would simply enforce the law on the books, and right now there is no such ban on those guns,” Chipman said.

Chipman, who left the ATF as a special agent and became an advocate at several gun control organizations, will face stiff opposition from Republicans as part of the political and social clash between advocates for gun rights and for preventing gun violence.

The confirmation hearing took place at the same time as a mass shooting at a San Jose railyard that authorities said left eight dead, along with the shooter, and reports of explosive devices in the building.

Chairman Richard J. Durbin of Illinois started questioning by giving Chipman a warning, and then a chance to address some false information, including an altered photograph to make it look like he was at the Waco siege in 1993.

“Buckle your seatbelt. You want to be head of the ATF, hang on tight. They’re coming after you, buddy,” Durbin said. “They’re creating some fictional stories about your life and your experience, and you’re going to have to weather this storm.”

Still, Republicans would need a Democrat to join them to stop Chipman’s confirmation.

In some ways, his nomination is a proxy for the deep policy divisions in the Senate, where Democrats have introduced bills to ban assault-style rifles and expand the background check system to purchase guns, and Republicans have stood in the way.

The panel’s top Republican, Sen. Charles E. Grassley of Iowa, said of Chipman that there “isn't a liberal hobbyhorse on guns that he hasn't ridden.” He said Chipman has been "misleading the public about modern sports rifles, arguing against popular magazine sizes or advocating for universal background checks.”

Grassley compared confirming Chipman as head of ATF to “putting a tobacco executive in charge of the Department of Health and Human Services, or antifa in charge of the Portland Police Department.”

Missouri Republican Sen. Josh Hawley asked, given Chipman's policy bias, how America’s hundreds of millions of law-abiding gun owners would have confidence he won’t try to restrict their Second Amendment rights.

“What assurances can you give them that you will limit your efforts to criminals who misuse weapons and leave law-abiding firearms owners to themselves?” Hawley said.

Chipman said that during his previous time at the ATF he saw gaps in the law that prevented the bureau from doing the job the American people expected it to do. So after he left the bureau he advocated for those changes.

“For 25 years, I enforced the law on the books. Every day me and other federal agents tried to catch the bad guys,” Chipman said. “That’s what the mission was, it was trying to keep the public safe.”

“Look at that 25 years, I was not going wayward with law-abiding gun owners,” Chipman said. “I never received a claim of that sort.”