"This is really a sea change in terms of how presidential candidates are talking about this, where they would not have in the past," Shannon Watts, Founder of Moms Demand Action for Gun Sense in America, told ABC News. "It was the third-rail of politics."
Compared to their GOP counterparts, the Democratic presidential contenders have a lot in common when it comes to gun control policy. But there are key differences in their proposals. Ahead of ABC News's Democrat debate this Saturday, here's a look at where they agree and where they don't:
IMPROVING BACKGROUND CHECKS:
Where They Agree: In the wake of the San Bernardino attack, all three Democrats agree the country should prohibit people on the FBI's no-fly list, also referred to as the ‘terrorist watch list' from purchasing guns. A measure to bar these purchases was blocked by Republicans in Congress recently, united Democrats on the issue even more.
In addition all three candidates talk about the need to improve the current system of background checks and close the so-called "gun show loophole," which would require gun dealers selling at shows and ad hoc venues to run background checks.
All three also call for action on what is referred to as the "Charleston loophole." Dylan Roof, who allegedly shot and killed nine members of an African-American church in Charleston this summer, was able to purchase a gun despite a previous felony, because of a long-standing default rule, wherein purchases can go through when law enforcement fails to complete a background check within three business days. Democrats are united on this issue and think this default to be abolished.
Where They Disagree: Clinton and O'Malley are specifically calling for universal background checks. O'Malley says he would seek to end Internet-sales all together and require all weapons purchases be made in person. Clinton says she would take "administrative action" to close the gun show and Internet-sale loopholes. Sanders has said the country must "strengthen and enforce" the instant background check system currently in place and that his campaign is in the process of assembling a more comprehensive package on gun control measures. While in the Senate, Sanders did vote in favor of a bill calling for universal background checks.
Where They Agree: All three candidates are calling for a ban on assault weapons and ending of the sale of high-capacity magazines. All three candidates also say they would make "straw purchases" (when one person buys a gun for another) a federal crime.
Where They Agree: All three have mentioned closing loopholes to make it harder for people convicted of domestic abuse or stalking from owning a gun, though Sanders has not laid out as many details on this as his opponents.
Where They Disagree: In addition to requiring buyers to pass a background check, O'Malley wrote in his policy position paper released in early September, that he wants everyone seeking a gun (whether through a sale or a gift or transfer) to "obtain a fingerprint-based license and complete safety training." He is also proposing a federal age requirement (21-years-of-age) for handgun ownership, and new requirements and definitions for safe home storage of firearms.
Where They Disagree: Clinton is also calling on the federal government to finish and enforce its rules to ensure the "severely mentally ill," involuntarily committed into treatment centers, are prohibited from purchasing guns.
MANUFACTURERS' LIABILITY AND DEALER LICENSING:
Where They Agree: Clinton and O'Malley are both pushing for the repeal of the "Protection of Lawful Commerce in Arms Act," which prevents victims of gun violence from suing gun manufactures or dealers for damages. Clinton voted against this bill in the Senate in 2005.
They also both promise to devote more attention and resources to gun store inspections, and empower and better fund the Bureau of Alcohol, Tobacco, Firearms and Explosives' ability to revoke licenses of non-compliant dealers.
Where They Disagree: Sanders voted in favor of the "Protection of Lawful Commerce in Arms Act," while serving in the House of Representatives. He has since said he is open to the bill being reevaluated.
Where They Disagree: O'Malley is the only candidate to date calling for the creation of a national firearms registry.
"This might be an easier issue for people to wrap their heads around if there was one easy answer, but like most complex public policy issues there isn't," Pia Carusone, spokesperson for Gabby Giffords's gun control PAC Americans for Responsible Solutions, told ABC News. "It is a series of actions that need to be taken by Congress, by the executive branch and all the way down to the community level in terms of supporting your local mental health center."
Moms Demand Action for Gun Sense says they will eventually endorse a candidate.
"These shootings are making single-issue voters out of mothers and women," Watts said, "In a perfect world, every single candidate will have something we can look at and compare. ... If you're caught off-guard and you don't have a policy or proposal on this, you look pretty tone deaf."
Editor's Note: “This article has been updated since its original publication after the O’Malley campaign provided further details regarding its position on straw purchases."