While the United States has been generally ahead of the curve in beefing up security as to cargo transported on passenger planes within the US, the risks involving cargo bound for the US from other countries remains substantial, as highlighted by the recent incidents involving cargo originating from Yemen. It's one thing for TSA to implement and enforce rules relating to cargo security within the US, but it will be very difficult to implement and sustain an effective screening process in foreign countries.
This recent article from The Houston Chronicle highlights the associated dangers and challenges (click here to read the full article).
A second article published online at Yahoo! Finance summarizes the tensions between the federal government and the major cargo carriers over the costs involved in implementing an effective screening program for cargo bound for the US (click here to read the full article).