The FBI ran 27.5 million gun-related background checks in 2016—about 4.4 million more than any other year on record.
The National Instant Criminal Background Check System processed 2,771,159 background checks in December, bringing 2016's total to 27,538,673, according to FBI records posted on Wednesday. That dwarfs the firearms check record of 23,141,970 set the previous year.
NICS firearms background checks are considered an accurate metric of gun sales.
The FBI processed twice as many firearms checks in 2016, the last full year of President Obama's administration, than it did in 2008, the year Obama was elected. During President Obama's eight-year tenure, the FBI has processed 157,233,157 firearms checks—61,249,149 more than the previous ten years.
Those figures have led some to label Obama "the greatest gun salesman in history." Gun rights activists have long argued that Obama, Hillary Clinton, and the Democratic Party's advocacy for gun control measures has fueled gun sales.
"2016 was mostly driven by fears that Hillary would win and the dangerous road we were already going down with Obama would continue," said Virginia Citizens Defense League President Philip Van Cleave.
"There is no doubt that President Obama's anti-gun rights agenda really backfired," said Alan Gottlieb of the Second Amendment Foundation. "All he accomplished was to set new records for firearm sales. He fueled the opposite of what the gun prohibition lobby wanted him to achieve. And I don't think they learned anything from it."
Activists pointed to Obama's executive actions and Hillary Clinton's promises of more aggressive action on guns as the main contributors to surging sales throughout the year. Clinton's assertion that the Supreme Court was "wrong on the Second Amendment," first reported by the Washington Free Beacon in 2015, was the subject of numerous campaign ads, as was her support for an Australian-style gun confiscation program, first reported by the Free Beacon a few days later.
Hacked emails revealed in October 2016 that the Clinton campaign considered her position on gun control to be the most forceful of any serious candidate in American history. She was defeated in November's election by Republican Donald Trump, who the National Rifle Association labeled "the most forceful Republican nominee for president in the last 100 years when it comes to not only gun ownership but the lawful use of guns for self-defense."
Terror attacks on American soil and abroad may also have increased sales of guns and ammunition.
"Unrest in the streets and terrorism were on the minds of many," Van Cleave said. "The risk of more unrest and terrorism continue to affect sales, as well."
While the number of checks run through the FBI's system is considered one of the strongest indicators for how many guns were sold in a given time period, the numbers don't represent an exact accounting of gun sales. A number of factors can affect the numbers, including the fact that many states use FBI checks during their gun-carry permitting processes, most states do not require FBI checks for gun sales between private citizens on the used market, and a single FBI check can facilitate the sale of multiple guns.
"These statistics represent the number of firearm background checks initiated through the NICS," the FBI said of its monthly background check report. "They do not represent the number of firearms sold. Based on varying state laws and purchase scenarios, a one-to-one correlation cannot be made between a firearm background check and a firearm sale."
The 2.7 million checks processed in December make the month the most active of 2016 and the third best month in the history of the system, but it also represents a sizable decrease from the 3.3 million checks recorded in December 2015. It also marks the first time in 20 months that gun-related background checks haven't set a monthly record.