The US Supreme Court in a 5-4 decision today stated that:
Warrantless searches “are per se unreasonable,” “subject only to a few specifically established and well-delineated exceptions.” Katz v. United States, 389 U. S. 347, 357.
(Arizona v Gant, 07-542, decided 4/21/09).
This was a case dealing with the 4th Amendment of the US Constitution, and more specifically, it concerned the warrantless search of a vehicle.
Hey isn't a wiretap and similar electronic surveillance a "search", and therefore a warrantless wiretap is a violation of the 4th Amendment?
In Olmstead v US in 1928 the US Supreme Court said no, electronic surveillance is not a search.
In Katz v US in 1967 the US Supreme Court overruled Olmstead, and said yes electronic surveillance is a search.
Any such electronic surveillance without a warrant is per se unreasonable.
Thus, in the NSA electronic surveillance cases (which include AT&T, Verizon, and some other telecoms as defendants) the burden should be on the government to show why all those NSA wiretaps without warrants are legal.
Warrantless wiretaps are per se illegal still according to today's ruling in the US Supreme Court.