The FBI's new domestic spying power

From the Washington Post (my emphasis):

Justice Department officials released new guidelines yesterday that empower FBI agents to use intrusive techniques to gather intelligence within the United States, alarming civil liberties groups and Democratic lawmakers who worry that they invite privacy violations and other abuses.

The new road map allows investigators to recruit informants, employ physical surveillance and conduct interviews in which agents disguise their identities in an effort to assess national security threats. FBI agents could pursue each of those steps without any single fact indicating a person has ties to a terrorist organization.

And lest we not forget the quaint Fourth Amendment to the Constitution:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.