You can't trust anybody

Not only was the whole thing a setup, but if this story is correct they never even took delivery of that ammonium nitrate.

Although police haven't officially said so, sources have told the Star's Michelle Shephard that the final act in the multi-year investigation came when federal agents intercepted the group's order for the fertilizer, and arranged to have it delivered by truck. But, the Star has learned, police switched the fertilizer with a harmless powder before making the delivery. After the deal was done, the handcuffs came out.

Now, none of this matters, legally. If you intend to make and explode a bomb, and you attempt to obtain the materials necessary to that end, then you're just as guilty whether or not you ever succeed in making the bomb and regardless of whether the materials turn out to be ammonium nitrate or baking soda. And no, it's not "entrapment" just because the police sell it to you, or pretend to. It's your intent that counts: to show entrapment, you have to show, in effect, that the police planted the thought in your brain -- that the idea of buying tons of ammonium nitrate and blowing up a building with it would never have occurred to you had the cops not cajoled you into it. But that stuff about the police having to move fast to prevent an imminent attack seems a bit over the top.