Let me start out with words advanced by both Justice Robert Jackson (chief American prosecutor at Nuremberg) and Justice Arthur Goldberg (U.N. Ambassador during the Johnson Administration after leaving the Court): The Constitution is not a suicide pact.
The premise of that statement is quite simple. Despite what we might like to think, there is no such thing as an absolute right. Rights end when they bring harm upon, and conflict with the rights of, others. For example, if your religion calls for you to go out and assault one person every day you will not be able to claim freedom of religion as a defense in the subsequent criminal trial. Instead, you will be convicted and, depending upon the severity and frequency, be sentenced to a term of incarceration.
This same premise holds true when it comes to national security and the responsibility of our government to keep American citizens safe. To start with, it must be asked what is the primary purpose behind the government action in question? Is it a standard criminal investigation with the ultimate of bringing a prosecution? Is it an attempt to collect intelligence to thwart a terrorist attack directed at United States citizens or at American soldiers?
The distinction between the two might not seem particularly important, but it actually is of the utmost importance. The former instance is exactly what the Fourth Amendment was designed to for to limit government power. Much of our Bill of Rights is inspired by (and lifted from) the English Bill of Rights, acceptance of which was a condition of William and Mary taking the throne. Another was the old English maxim that demonstrated the power of government to squelch dissent:
The latter, especially because it comes to matters of national security, affords the government some degree of greater deference, although not absolute deference.