Except for the definition and mechanism of proving treason, no area of the Constitution addressing the rights of all persons when the government is pursuing them is more specific than the Fourth Amendment. The linchpin of that specificity is the requirement that the government demonstrate probable cause to a judge as a precondition to the judge issuing a search warrant. The other specific requirement is identity: The government must identify whose property it wishes to search or whose behavior it wishes to monitor, because the Fourth Amendment requires that all warrants specifically describe the place to be searched or the person or thing to be seized.
The principal reason for these requirements is the colonial revulsion over general warrants. A general warrant does not specifically describe the place to be searched or the person or thing to be seized, and it is not based on the probable cause of criminal behavior of the person targeted by the government.
With a general warrant, the government simply gets authority from a judge to search a haystack looking for a needle, and in the process, it may disturb and move all the straw it wants. Stated differently, a general warrant permits the government to intrude upon the privacy of persons as to whom it has no probable cause of criminal behavior and without stating what it is looking for.
The Foreign Intelligence Surveillance Act (FISA) court has been issuing general warrants to the National Security Agency (NSA) since 1978, but it was not until last June that we learned that these general warrants have been executed upon the telephone calls, text messages, emails, bank records, utility bills and credit card bills of all persons in America since 2009.
The constitutional requirement of probable cause is not political fancy; rather, it saves us from tyranny. Probable cause is a quantum of evidence that is sufficient to lead a neutral judge to conclude that the person about whom the evidence has been presented is more likely than not to possess further evidence of criminal behavior, or has more likely than not engaged in criminal behavior that is worthy of the government's use of its investigatory tools such that the government may lawfully and morally invade that person's natural right to privacy.
Last week, Robert S. Litt, general counsel for the Office of the Director of National Intelligence, which runs the NSA, engaged in a curious colloquy with members of the president's Privacy and Civil Liberties Oversight Board. Litt complained that presenting probable cause about individuals to judges and then seeking search warrants from those judges to engage in surveillance of each of those individuals is too difficult.