Warrantless surveillance for the collection of foreign intelligence requires a different analysis. As an initial matter, it is widely accepted that the Constitution does not require that all searches be conducted pursuant to a warrant. The Supreme Court and lower federal courts have upheld warrantless searches in numerous settings. Searches incident to arrest, border searches, and vehicle searches, to name a few examples, may be conducted without a warrant. Warrantless searches of this sort must still, of course, comply with the Fourth Amendment’s reasonableness requirement. The federal courts have treated warrantless searches to obtain foreign intelligence analogously, holding that the Constitution does not require a warrant, although it does require that the searches be reasonable….