During WW II the government began to monitor and decode Soviet cables to/from the U.S. in a project known as "Venona" (sp?). From it they learned the Soviets had spies all over the U.S.
Now during the war the Soviet Union was our ally. In the context of the current controversy, was it wrong for the U.S. to be reading those cables?
Frankly I am of mixed feeling of the current controversy. This country was attacked and is in a state of war, so special procedures different than normal peacetime are appropriate. Some restrictions and surveillance make me uncomfortable (such as restricting domestic photography of infrastructure, e.g. taking pictures of buildings from the sidewalk), but others seem ok. If the recipient on the foreign end of a phone call is a possible enemy, then it seems proper for the govt military to monitor such communications. However, I would restrict any information gained for military purposes only.