Here is Chertoff's USA Today editorial. It provides a lot of explanation of the "broad" authority that they have and the importance of being able to search things but at no point does it directly engage the need for random searches without reasonable suspicion.

We cannot abandon our responsibility to inspect what enters the U.S. just because the information is on an electronic device. To do so would open a dangerous window for terrorists and criminals to exploit our borders in new and unacceptable ways.

And that is why we are now randomly inspecting international internet traffic! Oh, wait, we aren't, and in fact we just agreed to a new FISA bill that would require a warrant to do that... It turns out I have no idea what I'm talking about.

Opposing view: Searches are legal, essential - Opinion - USATODAY.com