President Obama used a rare Oval Office address Sunday evening to speak to a worried nation about the evolving threat of terrorism and the growing influence of the Islamic State.

One of the biggest messages the president tried to communicate to the American people was that a fear of terrorist attacks must not translate into a fear of all Muslims and spark unnecessary targeting. But judging by the immediate response after the speech, Obama did little to bridge the partisan divide.

Speaking from a lectern in front of his desk, the president called Wednesday's shooting in San Bernardino, Calif., that killed 14 people at a holiday workplace party "an act of terrorism designed to kill innocent people."

However, he didn't go so far to call it an act of "Islamic" terrorism, cautioning that even as a Muslim employee and his wife carried out the deadly attacks, there was "no evidence that the killers were directed by a terrorist organization overseas or that they were part of a broader conspiracy here at home."

Still, Obama did begin to acknowledge that there appeared to be some link between their connection with Islamic radicals and their actions, saying, "It is clear that the two of them had gone down the dark path of radicalization, embracing a perverted interpretation of Islam that calls for war against America and the West."

The shootings this past week follow last month's deadly attacks in Paris that killed 130 people, for which ISIS took credit. Obama added that terrorists' methods have evolved since the Sept. 11, 2001, attacks.

"As we've become better at preventing complex multifaceted attacks like 9/11," Obama said, "terrorists turn to less-complicated acts of violence like the mass shootings that are all-too common in our society. It is this type of attack that we saw at Fort Hood in 2009, in Chattanooga earlier this year and now in San Bernardino."

The growing influence of ISIS in particular, which has used social media and technology to expand its reach, has changed the dynamic. Skepticism of Islam has also been fueled, in part, by suggestions from some GOP presidential candidates such as Donald Trump, who has agreed with the idea of creating a database to register Muslims in the U.S.

But Obama emphasized that such backlash and division is exactly what the terrorist group wants.

"Let's not forget that freedom is more powerful than fear," the president said. "That we have always met challenges, whether war or depression, natural disasters or terrorist attacks, by coming together around our common ideals as one nation and one people."

Obama also detailed the ways in which the U.S. has already stepped up its efforts against ISIS, including training moderate Iraqi and Syrian forces, deploying more American special forces to the area and increased intelligence sharing with allies.

The president also said he would call for a review of visa-screening measures after one of the San Bernardino shooters was allowed into the U.S. on a fiancée visa.

And Obama also asked for Congress to officially recognize U.S. efforts in the fight against the terrorist group.

"If Congress believes, as I do, that we are at war with ISIL, it should go ahead and vote to authorize the continued use of military force against these terrorists," he said. "For over a year, I have ordered our military to take thousands of air strikes against ISIL targets. I think it's time for Congress to vote to demonstrate that the American people are united and committed to this fight."

Obama also called for stricter gun-control measures, something that has been met with heavy resistance by Republicans.

"To begin with, Congress should act to make sure no one on a no- fly list is able to buy a gun," the president said. "What could possibly be the argument for allowing a terrorist suspect to buy a semiautomatic weapon? This is a matter of national security."

He continued, "We also need to make it harder for people to buy powerful assault weapons, like the ones that were used in San Bernardino. I know there are some who reject any gun-safety measures, but the fact is that our intelligence and law-enforcement agencies, no matter how effective they are, cannot identify every would-be mass shooter, whether that individual was motivated by ISIL or some other hateful ideology."

Republican presidential candidates were quick to pan Obama's speech.

Responding on Fox News shortly afterward, Florida Sen. Marco Rubio said the president "said nothing new."

Texas Sen. Ted Cruz said in a statement: "If I am elected President, I will direct the Department of Defense to destroy ISIS. And I will shut down the broken immigration system that is letting jihadists into our country. Nothing President Obama said tonight will assist in either case."

Former Florida Gov. Jeb Bush called for a "war-time Commander-in-chief": "President Obama has finally been forced to abandon the political fantasy he has perpetuated for years that the threat of terrorism was receding."

Trump live-tweeted during Obama's speech — and wasn't impressed with the brevity of the president's 13-minute address.

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