This warning was raised by at least three Republican presidential candidates a day after a Muslim husband-and-wife terror tandem mowed down people celebrating a holiday party in San Bernardino, California, killing 14 people and injuring 17 others.

Senator Ted Cruz said, "This horrific murder underscores that we are in a time of war," CNN reported.

New Jersey Governor Chris Christie said, "We need to come to grips with the idea that we are in the midst of the next world war."

Florida Sen. Marco Rubio, for his part, said, "We're at war with jihadists."

Speaking at the Republican Jewish Coalition's presidential forum in Washington a day after the massacre, Cruz said, "All of us are deeply concerned that this is yet another manifestation of terrorism, radical Islamic terrorism here at home."

His thoughts were echoed by Christie, who is "convinced" that the shooting was indeed a terrorist attack. Christie slammed President Barack Obama for "wring(ing) his hands" by refusing to call the attack an act of terrorism.

However, Rubio was a bit more careful in his immediate reaction to the San Bernardino killings. "We don't know all the facts yet, but we certainly have learned some facts that are concerning," he said.

The senator from Florida later expounded during an interview with Fox News that gun control will not help the issue because it was not a workplace-related incident, other than the fact that the suspect "returned to their workplace and killed people there."

"They possessed dozens of pipe bombs. My sense is that these people were clearly planning a broader attack. He went back and said let's start it now because I'm upset," he said.

Rubio said he is more concerned about homegrown extremists since they are the "biggest danger we face."

He explained, "It's the likeliest way ISIS or al-Qaeda will attack our country and hardest to disrupt because these are not individuals that would have wound up on any database. These two people, these monsters that conducted this terrorist attack, are not people we would have known anything about until they did this."

Rubio said criminals will always have access to weapons, and this is why it is important for law-abiding citizens to have access to guns as well in order to protect themselves.

He said the United States must beef up its intelligence capabilities since it was diminished by recent legislation.

"Beyond it, you must destroy ISIS," he said. "You have to be clear that we're at war with ISIS. We're going to destroy their ability to spew propaganda and put out their online publication and to inspire people to attack us. We're at war with jihadists."