http://warisboring.com/articles/san-bernardino-killers-were-rare-hybrid-terrorists/Apparently the San Bernardino attack is rather confusing as it doesn't fit the definition of "regular" spree killers acts or terrorist attack and is a mix of both.
Unlike the San Bernardino killers, pseudocommandos often do not define their killings in ideological or political terms. In many cases, workplace killers and school shooters who “go postal” kill people whom they simply felt wronged them. It’s hard to call that terrorism.
On the other end of the spectrum, terrorist organizations such as the Islamic State have explicit political justifications for their atrocities, but the assailants often have little — if any — personal connection to their targets. They commonly choose crowded areas simply because that’s where the people are, though there also may be some symbolic importance.
...But instead, these attackers chose targets that they knew while their attack was clearly motivated by political reasons. ...Except that there is no link found to DAESh or any other terror group so far so these terrorist seem to be merely "fanboys." Meaning that, yes they did do this attack in the name of Islam but unlike the Paris attacks this was not something that was planned by a large terrorist organization that trained and armed the attackers. These people were just a few random people who decided to act for their cause.
The closest thing to something like this was a 2014 incident:
And if you think this is meaningless debate and we should just label this as Islamic terrorism and move on here is the problem:
How do we prevent something like this? Government agencies can spy on terrorists and try to find out if they are preparing an attack but if some loners or small groups with no connection to terrorists make plans like this (and there are plenty of guidebooks on the net) it is much harder to catch them.