It was an act of terror. Authorities didn't immediately place that label on Wednesday's attack in San Bernardino, Calif., in which the assailants sprayed a holiday party with hundreds of bullets, killing 14 people and wounding 21. But there is no better word than terrorism for such a bloody act of intimidation.

The assault was meant to terrorize, although exactly why is still under investigation. Radical Islamist ideology is suspected. CNN reported Friday that one of the assailants used Facebook to post a pledge of allegiance to Islamic State leader Abu Bakr al-Baghdadi. But there was no evidence as of Saturday that ISIS did more than provide inspiration for the carnage at a social services center booked by the San Bernardino County Public Health Department for a holiday potluck.

Syed Rizwan Farook, 28, and his wife, Tashfeen Malik, 27, apparently went to great lengths to hide their motivation, which stands in stark contrast to the many terrorists who have wanted their affiliations and grievances to be shouted to the heavens. The FBI says the couple deleted data from computers and damaged mobile devices to make their contents hard to recover.

But even if the attack, like so many other mass killings in this country, sprouted from a workplace grievance, ideology could have played a role. Farook, a health department inspector, reportedly once got into an argument over conflicting religious beliefs with a coworker who was a Messianic Jew, Nicholas Thalasinos. Thalasinos was among the shooting victims, but it wasn't known if he was targeted.

So much is unknown about this case, most glaringly why Farook and Malik chose to leave their 6-month-old baby with relatives so they could die together in a hail of bullets after shooting as many people as they could. They had been married only about two years after meeting through an online dating service. Farook sought "someone who takes her religion very seriously."

Malik was from Pakistan, which is where Farook's parents were born; he grew up in Riverside, Calif. The couple first met in person in Saudi Arabia. He obtained a 90-day visa to bring his fiancée to America, and she got a green card after they married. They lived a seemingly quiet life. Not even relatives suspected their home contained an arsenal of guns, thousands of rounds of ammunition, and at least a dozen homemade bombs.

That's scarier than any of the spooky suppositions posed by politicians peddling the notion that America must bar refugees fleeing war-torn Syria. Of course, safeguards must be in place, but homegrown terrorists are a more likely threat to this country than Islamic State moles posing as refugees. We can't close our borders to people already here, and the San Bernardino shootings show that it's impossible to unveil every potential domestic threat.

As authorities continue their investigation, America needs to figure out how to mute the siren song of ISIS. A George Washington University analysis shows that 56 Americans, including a North Philadelphia woman, have been arrested this year for ISIS-related activities. Each case is different, but political rhetoric that unjustly paints all Muslims with the same broad brush of suspicion can only increase alienation.