There’s a lot of half-baked commentary out there urging the Benghazi select committee chaired by Representative Trey Gowdy (R., S.C.) to “seize” forthwith the servers through which former secretary of state Hillary Clinton carried out her private e-mail scheme. Regrettably, some of it comes from lawyers and self-styled “constitutional conservatives” who ought to know better. As Chairman Gowdy explained to Megyn Kelly in a Fox News interview on Monday night, however, his committee — a legislative committee — is powerless to obtain search warrants and coerce the physical surrender of evidence.

Simply stated, the committee is not a prosecutor.

Our constitutional system is premised on the separation of powers. As I recount in Faithless Execution, the Framers were especially adamant that the power to make the law be separated from the power to enforce the law — the concentration of both in one set of hands being the road to tyranny. Consequently, Congress has no authority to conduct criminal investigations or to seize evidence. Those are police powers and they belong solely to the executive branch.