It has been four years since Congress made the bone-headed move of mandating 100 percent physical screening of passenger plane cargo. Serious risk management is not Congress’s bag, as the institution demonstrates often.

But for almost that long, DHS – which is all about risk management – compounded the error. First, the Department interpreted the mandate as applying to foreign-originating inbound cargo. This was a discretionary interpretive move that dramatically expanded the 100 percent mandate outside the United States, where enforcement is a practical impossibility.

Second, just when DHS interpreted the goofy mandate to apply to hundreds of airports outside U.S. jurisdiction, the Department declared (surprise!) that it could not enforce this mandate within the statutory deadline of August 2010, but would turn to the issue in due course.

Third, having declared the inbound mandate impractical, at least within the near term, DHS focused its air cargo security efforts on ensuring 100 percent screening for domestic air cargo. The Department used its substantial talent and resources on a bold and ultimately successful plan to ensure that all cargo flying from or within the United States is subject to physical screening. But this effort meant that for several years, DHS treated inbound air cargo as less risky than domestic air cargo. That does not comport with the common intuition that inbound cargo is riskier; in October 2010, the air cargo bombing plot, which used planes departing from Yemen, etched a very large data point on the side of intuition.

Fourth, after the inbound cargo bombing plot, DHS immediately declared that it would enforce the 100 percent mandate for inbound cargo by the end of 2011. DHS’s reaction to the bombing plot was understandable in some sense, but it conflicted with prior statements that enforcement of the 100 percent mandate for inbound cargo is impractical.

Fortunately, some elements within DHS sought to forge a new path, wisely piloting a program to conduct risk analyses of inbound air cargo and to focus DHS’s resources on the high-risk cargo, rather than attempting to subject all cargo to the same level of physical screening. This “risk-based” screening has been successful for DHS in other contexts, such as the screening of maritime cargo. And, now that the self-imposed end-of-the-year deadline for inbound cargo screening is almost here, DHS has dropped the pretense of ever being able to conduct 100 percent physical screening of inbound air cargo. Risk-based screening is the mantra.

But Congress, seeking to resurrect the original bone-headed move, is now applying the heat to DHS, repeatedly asking when DHS will apply 100 percent physical screening to inbound air cargo.

Let’s hope DHS stands its ground. These days, it’s all about risk-based screening – “100 percent” is soooo 2007.