As surely as the sun rises in the east, natural disasters periodically will blow Congress out of the headlines, and, just as surely, our representatives will try to weasel their way back into the papers by holding hearings. No doubt this impulse will obscure precisely what the goal of those hearings should be.

It is impossible to plan completely for this type of emergency and unreasonable to expect leaders to flawlessly execute what plans there are. Americans simply don’t see disasters of this magnitude often enough to be proficient in managing them, according to an associate professor of emergency management at the University of Richmond, Walter Green.

Consider the “failure” of the evacuation from New Orleans and the plight of the 100,000 people, mostly poor minorities, who didn’t make it out in time. Congress will hear charges that the evacuation was botched by local authorities who didn’t launch it soon enough and who didn’t follow plans for transporting the city’s most vulnerable inhabitants to safety.

According to Mr. Green, however, the fact that 80% of the population did get out is on par with mass evacuations in the past. Providing buses is only half the battle. The people most at risk are also the most reluctant to go: They’re least likely to trust government officials telling them to board the buses and most fearful about what will befall them if they leave their homes.

Likewise with efforts after the storm has come and gone. The slow response has been a hot point of criticism, but, as Mr. Green puts it, “no [planner] sits around dawdling and thinking up reasons not to go.” Frontline staff and middle managers – who are apt to face a catastrophe of this scope once in their careers, if that – must make snap decisions under intense pressure, including second-guessing from preening politicians.

That they’re bound to make mistakes is a lesson New Yorkers learned all too well on September 11, 2001, when the World Trade Center’s emergency evacuation procedures and the city’s heroic first responders were confronted with an unprecedented disaster. A calamitous hurricane passing through the Big Easy was more foreseeable. But a flood over four fifths of a city looks very different in reality than it does on paper in a disaster planner’s binder. Considering the challenges, Mr. Green says he would give the Katrina response a B, not an F.

Fruitful territory for Congress to consider includes how best to increase what Mr. Green calls the “visibility” of emergency managers – their working relationships with other officials, their ability to marshal resources, and the degree to which the public knows and trusts them. Also for Congress to consider is the question of how prevention resources are allocated, especially in light of an engrossing dispatch in yesterday’s Washington Post describing how for many years now Congress has used earmarks to force engineers to do just about everything but shore up levees around New Orleans.

Make no mistake, a city is submerged, hundreds of thousands of people are displaced, and emergency planners have fumbled. Our elected representatives have a lot to investigate, and those planners have some awkward questions to answer. But by the same token, a city is submerged and hundreds of thousands of people are displaced. Before the heads start rolling, Congress should remember that there’s only so much anyone could do.