The larger picture is this, since 9-11 the US has done very little to improve overall port security. According to a report I heard on the radio yesterday, less than 10% of the containers cominng into the US are really looked at anyway. We don't have enough large scanners or even radiation detection devices at the ports to cover everything as it stands.
Not to mention, that our intelligence agencies are still set up the same way they were pre 9-11, so we are still vulnerable to the same intel lapses & infighting.
Lastly, as far as ports go. Take a look at the Long Beac, CA port or the container port in Seattle, Wa. Those places are fucking huge and it's gonna take a hell of a lot of money, labor & other resources to scan, sniff, open, or other wise investigate a larger percentage of containers than we do now.