It's important to note that the adversaries are moving their targets away from the secure areas to the public areas of the airport. It is less about gaining access to a plane anymore than just causing damage, mayhem, and casualties wherever people may congregate. The selection of the American Airlines counter was no coincidence.
But it would be a mistake to try and push the limits and capabilities of the security and response personnel out too far away from the airport - say to the parking lot or beyond. Instead we should concentrate on what works for preventing and mitigating these attacks where we have the greatest capability to act and respond. Intelligence services had already warned of an impending attack in Belgium, that should have warranted a step-up in security. Second, the use of surveillance and behavioral detection is key to risk-based security - singling out those who are either in a surveillance or planning mode themselves, or those acting in any way unusual. Security awareness teaches us not to ignore anything suspicious, out of place, or that gives us unease. These skills should not be cultivated by security and law enforcement alone - they are ones we all need to develop and use.
Lastly, we also need to be aware that terrorists will use whatever means they have at their disposal. In Europe, the terrorists rely on bomb-making expertise and materials gained in Iraq and Syria - things that are much harder to come by in the US, where guns and rifles are more easily obtained (homemade pressure cooker or pipe bombs notwithstanding). The US has also been more successful in infiltrating and monitoring terror cell networks here than the Europeans have, owing greatly to the fact that we are a much more integrated society.
In the meantime, we should expect a period of heightened security around transportation and other critical facilities, but we should continue to be vigilant even after the crisis is no longer fresh in our minds. - TH