Clinton told a crowd of supporters in New Hampshire on Thursday that she would "not be silenced" on gun violence.
Sanders, who earlier in his career was backed by the National Rifle Association, issued a statement from his Senate office calling for an assault weapons ban, new limits on high-capacity magazines, tougher background checks and other limits. Sanders won his first election to Congress with the help of the NRA and has voted against gun control bills throughout his career, but the group later came out against him in 1994.
Gun control had been a flashpoint between the two Democrats before
, including some sniping between the two during their first debate which led to charges Sanders was being sexist. But after Wednesday's shooting they found themselves on the same page -- and also in stark contrast to Republicans who pointed the finger at mental health issues and radical Islam in the wake of the shootings.
Syed Rizwan Farook and his wife, Tashfeen Malik, carried out the San Bernardino shooting massacre, according to investigators. Law enforcement officials said Thursday that Farook was apparently radicalized and in touch with people being investigated by the FBI for international terrorism.
That radicalization, sources told CNN, contributed to his role in the mass shooting of 14 people Wednesday during a holiday party for the San Bernardino County health department. The couple carried two .223-caliber rifles and two pistols, all of which were purchased legally, according to San Bernardino Police Chief Jarrod Burguan.
"They should not have been able to do this," no matter "what motivated" the shooters, Clinton said. "I don't believe we can stop every incident of gun violence but we sure can stop a lot of them ... We need to take action now."
Clinton also defended Muslim Americans during her forceful remarks, telling the audience at an event focused on women in business that "the vast majority of Muslim Americans are just as concerned and heart broken about this as anyone else."
At an event later Thursday, Clinton said the emerging picture surrounding the incident pointed to "terrorism."
"I have confidence that the local police, working with the FBI, we will learn more about what went on and who these people were and what their motivation were. But it is becoming clearer that we are dealing with an act of terrorism."
Sanders said Thursday that mass shootings had reached "epidemic levels" this year.
"It is very difficult for the American people to keep up with the mass shootings that we seem to see almost every day. Yesterday, San Bernardino, a few days ago, Colorado Springs, before that Roseburg, Oregon, before that Chattanooga, Tennessee, and on and on it goes," Sanders said in a statement. "The San Bernardino shooting was the 355th mass shooting this year. Gun violence has reached epidemic levels in the United States."
Sanders said Congress should pass gun control measures largely sought by Democrats. But he also threw his support, however, behind an answer being pushed more by Republicans: mental health care reforms.
"The sad reality is that in America today there are many thousands of people who are walking our streets who are suicidal or homicidal. And these people need treatment when they need treatment, regardless of their income, regardless of their insurance status," he said.
Clinton has been outspoken about gun control
for much of her campaign, focusing on the issue and repeatedly calling for "common sense" gun control. After the nine people were killed in a Charleston, South Carolina, church, Clinton said the United States has to "keep weapons out of the hands of criminals and the violently unstable while respecting responsible gun owners."
As she has done repeatedly, Clinton blamed Congress for inaction on guns.
"Just what will it take for Congress to overcome the intimidation of the gun lobby and do something as sensible as making sure people on the terrorist watch list can't buy weapons," Clinton said. "If you are too dangerous to fly in America, you are too dangerous to buy a gun."