Jeffrey Bellin’s article, Crime Severity Distinctions and the Fourth Amendment: Reassessing Reasonableness in a Changing World, argues that the severity of the crime under investigation ought to be taken into account in assessing both the reasonableness of searches and whether a government action is a search in the first place. In pursuit of this objective, his article provides the best attempt to date at dealing with the difficult issue of separating serious from not-so serious crimes (he ends up with three categories—grave, serious and minor. He then makes the enticing argument that calibrating the degree of Fourth Amendment protection according to crime severity would allow courts to provide more protection for those suspected of minor crimes because courts will no longer fear that such a move will handcuff police investigations of serious crimes. My concern is that just the opposite will occur. Rather than starting from a baseline of warrants and probable cause for investigations of serious crimes and ratcheting protection upward as the targeted crime becomes less serious, courts are likely to apply the warrant baseline to minor crimes and ratchet protections downward when law enforcement goes after people suspected of being terrorists, murderers, rapists and robbers. The proposition that the state should be barred from investigating minor crimes—which appears to be Professor Bellin’s agenda, at least when the investigative technique is perceived as “intrusive”3—will be too hard for courts to swallow, because it amounts to judicial crime definition in the substantive due process tradition the courts have rejected. At most, courts will require the full complement of probable cause and a warrant in such situations. At the same time, if reasonableness analysis incorporates a crime severity component as Professor Bellin proposes, courts will inevitably relax those requirements in a wide array of investigations, probably involving intermediate, “serious” crimes as well as “grave” crimes (to use Professor Bellin’s categories).