Does this change the essence and usage of public spaces, transit, or other significant targets, or is it something that is impossible to think about and lead a somewhat normal existence? It's heartening to see that the law enforcement and intelligence is working to find these plots and protect people from all areas from danger. It is easy to become complacent as residents (and maybe that's a good thing, as living in fear of the possible dangers would make it hard to leave the house in the morning) - so the hidden network of danger seems to become distant - happening elsewhere around the world, or sometimes creeping into the large cities of the United States. Oklahoma City proved that high profile targets are sometimes not what we think, and the enemies may not come from outside. The danger, everywhere is real.
Beyond the continuing efforts of law enforcement, how, if at all, do we react, and how does this impact the form and function of cities? Do we evolve more security and barricades? Disallow the gathering of large groups? Do public spaces become less public?
More cameras, surveillance, metal detectors? Is transit, which creates density of people, perceived as dangerous - making people flee to the 'safety' of the singular car? While not the Green Zone in Baghdad, it's interesting to see how this shapes the modern city. The securing of buildings has definitely received plenty of attention - and the ability to control access points, beef up materials, essentially defend an object. While much has been made of federal building security, making a better, more stylish bollard, is still using a bunker mentality that isn't really applicable for public spaces.
It's a bit different when operating in open space, as there are infinite entry points, making the perimeter harder to defend. I was thinking of precedents, and immediately looked at the well-publicized, award-winning security measures for the Washington Monument. While inventive in the way it doesn't detract from the monument itself, and while technically more open, this is merely a different version of the bunker protecting an object - not a way to secure outdoor public space - surrounding walls, underground tunnels forming a perimeter around the monument.
In the end, the author concludes that public space is too important to abandon for fear of attacks. Community matters.