Terror By Paralysis
This sort of thing will become common.
Far better we collapse as a nation than allow a few Muslims to be delayed from immigrating.
First, there is ample evidence that ISIS has a number of operational cells in the U.S. Lt Gen Flynn (former DIA director) said last month that the terrorist group likely has a C2 network inside our borders. No much point in building that sort of network unless there are operational assets to control/direct.
Secondly, no one really believes the San Bernardino shooters were able to plan and train for their deadly mission on their own. Neighbors saw a number of Middle Eastern men come and go from their residence, and the group spent lots of time in the bomb factory...er, garage. Quite possible those other folks are trainers or facilitators. It would be very unusual for terrorists from other cells to meet with the shooters, since ops at that level are strictly compartmentalized. Finally, we don't know what the FBI and the intelligence community have discovered in the aftermath of San Bernardino. But that information, coupled with the threat received by the LAUSD board member, was enough to shut down the entire system.
This was probably just a dry run; ISIS wants to see how authorities react, including their search patterns, and compare those to schools on the target list. Schools visited by Farook will probably receive extra scrutiny during the search, so the terrorists will simply shift to other targets.
Years ago, the Israelis had a problem with Palestinian terrorists targeting schools. The education establishment asked the IDF for help, but the military said they didn't have enough soldiers to cover all the schools--in a nation with compulsory military service for almost everyone, and large numbers of citizens who are firearms experts and trained in counter-terrorism. The IDF suggested arming teachers and the school authorities agreed. There are armed Israeli teachers in every school and there hasn't been a terrorist attack against a public school in decades.