Hillary Clinton (Brian Snyder/Reuters)

A sharp political debate broke out Sunday among the presidential candidates in the 2016 race over what lessons to take from the mass shooting in San Bernardino, Calif., and whether tighter gun laws, better intelligence-gathering or a more-aggressive fight against the Islamic State terrorist group could help prevent more carnage.

Although the United States has long been divided over gun laws and national security, the latest massacre — an act of pre-planned terrorism that also bears the confused markings of a random workplace attack — has only muddled the question of which debate is more pressing. That adds to the challenge facing President Obama, who on Sunday night will address the nation from the Oval Office for only the third time of his presidency.

The address comes amid mounting criticism of Obama’s strategy to defeat the Islamic State and his refusal to alter course despite evidence showing that the militant group’s ability to sow terror beyond its home base has expanded in recent weeks. Attorney General Loretta E. Lynch said Sunday morning on NBC’s “Meet the Press” that there were “indications of radicalism” in the San Bernardino attack. But her staff members also told NBC that Obama’s address tonight will call on Congress to look at certain gun-control measures.

Speaking on ABC’s “This Week,” Democratic presidential front-runner Hillary Clinton tried to strike a similar balance, saying that the United States needed to intensify its efforts against the Islamic State while also highlighting gun laws that allow “easy access” to weapons by fugitives, felons and those on the terrorism watch list.

On the same show, Republican candidate Jeb Bush said the talk of guns was misplaced. “The first impulse of Hillary Clinton and Barack Obama is to have gun control. Let’s have a strategy to take out ISIS there so we don’t have to deal with them here,” he said, using an acronym for the Islamic State.

On the Sunday after 14 people were shot to death in San Bernardino, Calif., presidential hopefuls weigh in on proposals for dealing with gun restrictions, including an amendment - rejected by the Senate - that would ban individuals on the terror watch list from buying guns. (Sarah Parnass/The Washington Post)

In a separate Sunday morning interview on CBS’s “Face the Nation,” Republican candidate Donald Trump said the attack in California and an earlier slaughter in Paris might not have been so deadly if the assailants’ victims also had been armed.

“You look at Paris, no guns — nothing,” Trump said. “And you look at California, no guns. I can tell you one thing, if I’m in there and had a gun, we’re going down shooting. We’re going to knock them out, okay? One way or another.”

But in this case, he said, “only the bad guys had the guns. So they were like sitting ducks, every one of them.”

The policy questions about terrorism and guns in the aftermath of the San Bernardino shooting largely cut along party lines, and the way in which these debates play out could help to define the 2016 presidential race. In recent days, many Republicans have argued that the United States and other Western nations have failed to stop the spread of the Islamic State in Iraq and Syria; one GOP candidate, Sen. Ted Cruz (Tex.), said Saturday that if he were elected, “we will carpet-bomb [the Islamic State] into oblivion. I don’t know if sand can glow in the dark, but we’re going to find out.”

Democrats, meanwhile, have tried to use the moment to push ahead with long-stagnant gun legislation, even though tighter regulations have failed in Congress in the aftermath of other mass shootings. On Thursday, the Senate voted against a bill proposed by Sen. Dianne Feinstein (D-Calif.) that aimed to deny people on the federal terrorism watch list the ability to purchase guns. Feinstein took the 54-to-45 defeat as a sign that Congress is a “hostage to the gun lobby,” she said in a statement.

“If you’re too dangerous to board a plane, you’re too dangerous to buy a gun,” Feinstein said.

Investigators are racing to piece together the motives for the San Bernardino mass shooting, in which a husband-and-wife tandem used semiautomatic weapons to kill 14 and injure 21 at a holiday party for local government workers. One of the shooters, Tashfeen Malik, who came from Pakistan and grew up in Saudi Arabia, wrote on Facebook before the attack a pledge of allegiance to the head of the Islamic State. Still, no indications have surfaced of more formal ties to terrorist groups or cells.

For Obama, the rare Oval Office address — his first since 2010 — comes amid concern in the West Wing that terrorism threats to the United States will overtake the rest of Obama’s agenda in his final year in office and lead to policy decisions in Congress that could exacerbate the problem.

The president has ruled out deploying significant U.S. military troops to the region, relying instead on airstrikes from a U.S.-led coalition and providing assistance to local forces in Iraq and Syria. Obama and his advisers have pointed to success in some areas of Iraq, where the Islamic State has lost territory. But the string of recent attacks claimed by the Islamic State — including the downing of a Russian airliner over Egypt’s Sinai Peninsula and the terrorist rampage in Paris — have alarmed the public and led Republicans to charge that Obama has underestimated the group.

National security adviser Susan E. Rice defended the administration’s approach Sunday, saying that the effort to retake territory from the Islamic State is aimed at making the group’s goal of establishing an Islamic caliphate appear less attractive to foreign fighters who have flocked to the region.

“It will take time, and success will not be linear. We must focus on Iraq and Syria but not exclusively. We see ISIL in other parts of the world,” Rice said in an interview with CNN, using another acronym for the militant group.

The setbacks have put Democrats, including Clinton, in the uncomfortable position of being asked to second-guess Obama.

On ABC, Clinton said: “We have to fight in the air, fight on the ground and fight them on the Internet. We have to do everything we can with our friends and partners around the world. That’s what we’ll hear from the president, to intensify the current strategy.”

She added that they must also take additional steps, including asking Facebook, YouTube and Twitter not to allow Islamic State fighters to post messages appealing to potential sympathizers around the globe.

But, she emphasized, “I don’t think there should be American combat troops. . . . That would make things worse.”

Trump, on Sunday morning, focused more on how to prevent future attacks from occurring on U.S. soil and said he would go after family members of known extremists and find out what they know. Trump also lamented the unwillingness of many Americans to report suspicious behavior among Muslims to police — something Trump blamed on political correctness.

Earlier, also on CBS, the sister of San Bernardino shooter Syed Rizwan Farook had apologized in a teary interview, saying she didn’t know about the plot of her brother and his wife. Trump said he didn’t believe the sister, Saira Khan.

“I would go after a lot of people, and I’d find out whether or not they knew,” Trump said. “I’d be able to find out. I don’t believe the sister.”

Vanessa Williams and Juliet Eilperin contributed to this report.