Should someone on the terror watch list be able to buy a gun?

Senate Democrats passed on an opportunity earlier this week to restrict the sale of guns to suspected terrorists, a tactical move that illustrates the deep divide between lawmakers on issues of national security and gun control.

The measure, which would have established a 72-hour delay on gun purchases by anyone on the national terror watch list, offered a rare opportunity for Congress to unite behind legislation addressing both gun violence and terrorism. But Democrats refused to embrace the Republican measure after their GOP colleagues shot down an outright ban on gun purchases by anyone on the watch list.

This latest legislative debate highlights the ongoing battle between proponents of more gun control and advocates for unrestricted constitutional rights. The perennial fight is complicated by fears of home-grown terrorism in the wake of the Dec. 2 terrorist attack that left 14 dead and 21 wounded in San Bernardino, Calif.

Sen. Chuck Schumer, D-N.Y., called it “absolute insanity” that persons on the watch list can legally purchase firearms. He cited a U.S. Government Accountability Office report finding that between 2004 and 2014, people on the watch list legally purchased guns 2,043 times out of 2,233 attempts—a 91 percent success rate.

“Given what happened in San Bernardino, it is extra insanity that we are not going to move on this,” he said.

But Sen. John Cornyn, R-Texas, said he was “astonished by the proposition … that you can be on a secret watch list by the federal government, and just by virtue of this secret listing of an individual on a government watch list, you can be denied some of your core constitutional rights.”

As an alternative to the full ban, Cornyn proposed granting the U.S. Justice Department 72 hours to intervene when someone on the terror watch list tries to purchase a gun.

Neither measure would have stopped the San Bernardino attackers from obtaining their weapons, some of which were purchased by a friend. But neither of the shooters was on any government watch list.

National security concerns represent a new angle in the broader gun control conversation, which Senate Republicans have tried to focus on mental health. In August, Cornyn introduced a bill backed by the National Rifle Association that has the potential to divide Americans who support both the Second Amendment and states’ rights. According to Business Insider, the bill would award a 5 percent funding boost in law-enforcement grants to states that forward 90 percent of their records on mentally ill people to the National Instant Criminal Background Check System. Conversely, states that refuse could see funding decrease.

Gun control is likely to remain center stage throughout the 2016 presidential election cycle and the final year of President Barack Obama’s term. Democratic frontrunner Hillary Clinton has promised to continue highlighting the issue. White House officials announced Thursday the president is preparing to take executive action to circumvent Congress in closing the “gun show loophole” that exempts attendees and online buyers from background checks. The push for tighter restrictions follows a Black Friday on which a record number of Americans submitted to an FBI background check while purchasing a gun.

The Associated Press contributed to this report.