When federal agents appear at the door, the most prudent response is to say, “Talk to my lawyer.” Just ask Zack Bonfilio. Local law enforcement and the FBI are using a new tactic: the “knock and talk.” Pairs of agents are appearing on Americans’ doorsteps unannounced, uninvited, and invariably without a warrant, with the aim of gaining access. For what exactly? Information. Visual surveillance. Property searches. And the Fourth Amendment’s protections against warrantless searches? Authorities don’t seem terribly concerned. According to the Rutherford Institute, “knock and talk” actions are initiated at private citizens’ homes without warning, often in the early...