"I think it's symptomatic of the broader issue -- almost a hope that none of this is terror-related, because he wants the argument to be that we've got this under control," the Florida senator said on Fox News' "Fox and Friends." "We don't have this under control."
Authorities say Syed Rizwan Farook and his wife Tashfeen Malik -- one, a U.S. citizen and the other, a permanent resident — shot and killed 14 people at a holiday party at the Inland Regional Center in San Bernardino, California. Both were killed in a police shootout, and officials said thousands of rounds of ammunition and 12 pipe bombs were found in the couple's apartment.
"My sense of it is that these people were really planning a broader attack but I think the evidence is going to continue to show that these were clearly people that had been radicalized," Rubio said. "You don't build all these pipe bombs and set up booby traps unless you're planning something."
The fact that one of the suspects was a U.S. citizen justifies fears about home-grown terrorism, Rubio said.
"These are not the individuals who would have wound up on any database," he said. "These are not people we would have known anything about until they did this."
The 2016 presidential candidate argued that rebuilding our country's intelligence capabilities would be a major step in defeating terrorism.
"You must destroy ISIS. We've got to be clear -- we are at war with ISIS. We are at war with radical, apocalyptic jihadists. And that is why ultimately we must defeat them," he said.
Obama said Thursday it is possible the shooting was terrorist related but also said it's also possible that it was "workplace related," adding that it's possible there were "mixed motives" behind the incident.
Making it more difficult to get a gun will not decrease gun violence nor would it have disrupted the San Bernardino incident, Rubio argued.
"Criminals will always have access to weapons. That's why it's important that law-abiding citizens have access to protect themselves," he said.