Authorities evacuated the surrounding block and a mall nearby due to the potential threat.
The status of Chuck Canterbury, a former national president of the Fraternal Order of Police, had been in limbo for months after a number of conservatives disapproved of his nomination by President Donald Trump to lead the Bureau of Alcohol, Tobacco, Firearms and Explosives last year.
"She became consumed with the Columbine and Oklahoma killings," the Hillsborough County sheriff said.
"If you asked most Americans whether they believe there are standards in place to secure weapons in gun shops, I would suspect most Americans would say yes," Congressman Joe Morelle told Newsweek.
Representative Earl Blumenauer of Oregon introduced a bill to regulate marijuana the same way the government currently regulates alcohol products.
An ATF official said the agency did not believe the suspected theft was terrorism-related.
Donald Trump blamed Hillary Clinton's "animals" for the incident.
All dealers selling guns—whether at shows, in flea markets, on the Internet—are required to get licenses and run background checks on buyers.
Even in a country where more people own more guns than anywhere else in the world, Brent Nicholson's cache is extraordinary
The White House is reconsidering its plan to prohibit a popular brand of rifle bullets after it came under fire from lawmakers and others.