Months later, the insurgent candidate has failed to live up to that pledge.
Sanders' campaign has yet to issue a detailed policy paper on gun control, something the candidate has done for a slew of other economic and core-Democratic issues. And his campaign does not list fighting gun violence on his more than 20-position-long issue page
on his website.
Sanders' aides did not respond to multiple requests about why his campaign has not announced a "comprehensive" gun plan as promised.
Gun control has been a nagging issue for Sanders since he launched his campaign last year. While Sanders has appealed to the left of the party on campaign finance, education and health care, guns are one issue that Hillary Clinton has successfully used to hurt Sanders' liberal bona fides. That matters in a state like South Carolina, where the Vermont senator still needs to grow his base of support.
Clinton's campaign has hammered Sanders on gun control, telling voters that while the Vermont senator talks about standing up to powerful interests, he has failed to do that with the National Rifle Association and the gun lobby.
Most notably, Sanders voted against barring the Centers for Disease Control and Prevention from studying gun violence in 1996 and voted against versions of the Brady Handgun Violence Prevention Act five times from 1991 to 1993.
Sanders has called the Clinton attacks on guns "very disingenuous."
"I have a D-minus voting record from the NRA," Sanders said during a January debate in South Carolina. "I support what President Obama is doing in terms of trying to close the gun show loopholes."
Clinton has focused on the issue for much of her campaign, pledging to close a series of gun control loopholes and revoke licenses from bad actor gun sellers.
Sanders' most comprehensive statement on guns came shortly before the January debate, when the senator reversed his position on a 2005 Senate vote that gave gun manufacturers immunity from prosecution. As a member of the House of Representatives at the time, Sanders voted in favor of that bill.
"I'm pleased that this legislation is being introduced," Sanders said of Sen. Richard Blumenthal and Rep. Adam Schiff's proposal to take away immunity from gun manufacturers when their products are used in crimes. "As I have said for many months now, we need to look at the underlying law and tighten it up."
Sanders has declined to call the 2005 vote a mistake a number of times, citing the fact that he worries about the impact rescinding immunity would have on small, family-owned gun shops.
In supporting the legislation, Sanders also said he would propose an amendment to the bill that "would require the Commerce Department to monitor and report on the law's impact in rural areas on the availability of hunting supplies, including firearms, sold by non-negligent local gun stores."
In the face of public pressure after mass shootings, Sanders said last year that "the status quo clearly is not working and people on both sides of this issue cannot simply continue shouting at each other."
But the Vermont senator has tempered his usual fire and bluntness when it comes to guns, stressing a more cautious approach to addressing mass shootings.
"If somebody has a gun and it falls into the hands of a murderer and that murderer kills somebody with the gun, do you hold the gun manufacturer responsible?" he asked at the Democratic debate in Las Vegas in October. "Not any more than you would hold a hammer company responsible if somebody beats somebody over the head with a hammer. That is not what a lawsuit should be about."