In the wake of the horrific elementary-school shootings in Newtown, Conn., last month, many Americans, desperate to do something in response, have decided that much stricter gun control is the answer. Democrats have proposed reinstating the 1994 Assault Weapons Ban, and Sen. Dianne Feinstein has proposed legislation that would even restrict the use of some semiautomatic handguns.

As a former prosecutor in Washington, D.C., who enforced firearms and ammunition cases while a severe local gun ban was still in effect, I am skeptical...