In 2004, the FBI mistakenly believed that Brandon Mayfield, an Oregon lawyer, was linked to the Madrid train bombing. Since the government claimed foreign intelligence was involved in the criminal investigation, the FBI - under new Patriot Act powers - obtained warrants from the secret intelligence court and covertly searched Mayfield’s home and office without ever having to prove “probable cause

Before the Patriot Act, the standard for obtaining a warrant for foreign intelligence surveillance was proof that the government’s primary purpose was gathering intelligence, not investigating a crime. However, under the Patriot Act, that standard has been lowered, and the government can get a warrant as long as foreign intelligence is one of its significant purposes. This change essentially allows the FBI to conduct searches and wiretaps - even where the primary purpose is to investigate a crime - without first demonstrating probable cause, thereby evading Fourth Amendment protections. The Mayfield case shows that the government is quite willing to take this shortcut, so it’s good news that the court has called off this end run around basic constitutional rules.

This week’s ruling – and another earlier this month striking down the Patriot Act’s national security letter provision – once again demonstrates that the Patriot Act fails to strike the right balance between protecting the nation and protecting individual liberties. There is no reason why the FBI can't investigate criminal activity - including terrorism - while complying with the Constitution.