It brings to mind the Times Square bombing two years ago, which led to the shattered windows and busted glass door in the famous Army recruitment office. I took the photo above when I'd been working in the area, and in fact was shook out of a sound sleep at about 4AM by the blast. More details on that bombing are here, and a later update is here. The suspect in that bombing was never caught.
(UPDATE: The license plate used on the vehicle has been traced to an auto recycling business about 3 miles from my home. Weird.)
Why did this attempted attack occur now? Well, just look at how the hate rhetoric has ratcheted up lately, with the implied encouragement of ultra-conservative Republicans and Fox News pundits. Tea baggers are openly carrying firearms to Tea Party rallies; not for any valid sporting purpose, but solely to intimidate the less radical percentage of the population.
Timothy McVeigh is an example of what happens when anti-government feelings are fostered. The impulse to strike out or "get even" with the government for real or imagined transgressions is subtly encouraged. There are people who, after being exposed to hours of programming daily which is relentless in it's message against the government, may act out on their own.
Fortunately, the vehicle bomb seems to have been amateurishly designed and constructed. Somehow it failed to fully ignite, almost certainly sparing the lives of many innocent bystanders. I'd guess it was designed by a couple of yokels in a barn somewhere and wasn't the work of a highly sophisticated organization.
As for the motive? As I said, it's still very early in the investigation, but I wouldn't be surprised to hear, if and when the suspects are caught, that it turns out to have been the work of
UPDATE: Okay, I was wrong; it was a naturalized US citizen from Pakistan.
But really, what were you supposed to think when they kept showing that surveillance video of the middle-aged balding white guy taking off his shirt in Times Square? That guy totally fits the stereotypical tea bagger profile!