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.

It occurred to me when driving home that there are two assertions made in this editorial that aren't true.

As a practical matter, travelers only go to secondary when there is some level of suspicion.

That is a lie. Customs selects people at random and they have quotas for secondary screening that they must meet. I know this because I was personally selected for secondary screening at LAX and the officer who did so indicated to another officer at the time that they had met their quota.

Yet legislation locking in a particular standard for searches would have a dangerous, chilling effect as officers' often split-second assessments are second-guessed.

That is also a lie. Reasonable Suspicion is a standard that is so thin that really any rationalization that an officer had for flagging someone would likely be upheld. The reason it ought to be required is so that they cannot perform searches at random and they cannot operate quotas.