On Saturday President Donald Trump accused former President Barack Obama of tapping his phones at Trump Tower in the month before the election. Trump is presumably basing his assertion on reports that the Justice Department under Obama applied for a warrant under the Foreign Intelligence Surveillance Act (FISA) to conduct surveillance on Trump associates.

Here are ten things you should know about the federal law at the heart of this controversy:

1. The Foreign Intelligence Surveillance Act of 1978 (FISA) is a federal law that outlines procedures for conducting physical and electronic surveillance in the name of national security and for the collection of foreign intelligence information.

2. FISA was introduced by Sen. Ted Kennedy as part of a Congressional response to findings that the U.S. government had abused the privacy rights of certain American citizens. Those abuses had occurred, according to the government, as part of its efforts to counter purported threats to national security. President Jimmy Carter signed FISA into law on October 25, 1978.

3. FISA has been expanded and broadened by several amendments: the Intelligence Authorization Act of 1995, the Intelligence Authorization Act of 1999, the USA PATRIOT Act, the USA PATRIOT Additional Reauthorization Amendments Act of 2006, the FISA (Foreign Intelligence Surveillance Act) Amendments Act of 2008, and the FISA Sunsets Extension Act.

4. Initially, FISA addressed only electronic surveillance but has been significantly amended to address physical searches, business records, and the use of pen registers and trap and trace devices. (As defined by U.S. law, the term “pen register” means a device or process which records or decodes dialing, routing, addressing, or signaling information transmitted by an instrument or facility from which a wire or electronic communication is transmitted. The term “trap and trace device” means a device or process which captures the incoming electronic or other impulses which identify the originating number or other dialing, routing, addressing, and signaling information reasonably likely to identify the source of a wire or electronic communication.)

5. FISA also established the United States Foreign Intelligence Surveillance Court (FISC), a special U.S. Federal court that holds nonpublic sessions to consider issuing search warrants under FISA. The court is comprised of eleven federal district court judges, selected by the Chief Justice of the United States, who serve for staggered, non-renewable terms of no more than seven years. The judges of FISC travel to Washington, D.C. to hear warrant applications on a rotating basis. (To ensure that the court can convene on short notice, at least one of the judges is required to be a member of the U.S. District Court for the District of Columbia.) The eleven judges must be drawn from at least seven judicial circuits, and no fewer than three are to reside within twenty miles of the District of Columbia.

6. Warrant applications under FISA are drafted by attorneys in the General Counsel’s Office at the National Security Agency at the request of an officer of one of the federal intelligence agencies. Each application must contain the Attorney General’s certification that the target of the proposed surveillance is either a “foreign power” or “the agent of a foreign power” and, in the case of a U.S. citizen or resident alien, that the target may be involved in the commission of a crime.

7. FISA contains one exception to the requirement for a court order: The President may authorize electronic surveillance to acquire foreign intelligence information for periods of up to one year without a FISC court order when the Attorney General certifies that there is “no substantial likelihood that the surveillance will acquire the contents of any communication to which a U.S. person is a party,” provided the surveillance is directed solely at communications among or between foreign powers, or “the acquisition of technical intelligence … from property or premises under the open and exclusive control of a foreign power.”

8. As defined by FISA, a “foreign power” means a (1) foreign government, (2) a faction of a foreign nation, (3) an entity that is openly acknowledged by a foreign government or governments to be directed and controlled by such foreign government or governments, (4) a group engaged in international terrorism, (5) a foreign-based political organization, (6) an entity directed and controlled by a foreign government, or (7) an entity engaged in the international proliferation of weapons of mass destruction. (Each of these conditions are qualified by being “not substantially composed of United States persons.”) As defined by FISA, “agent of a foreign power” includes any non-U.S. person who (1) acts in the United States as an officer or employee of a foreign power, (2) acts for or on behalf of a foreign power which engages in clandestine intelligence activities in the U.S., (3) engages in international terrorism, (4) engages in the international proliferation of weapons of mass destruction.

9. The Intelligence Reform and Terrorism Prevention Act of 2004 amended the definition of “agent of a foreign power” in FISA to add a new category of covered individuals known as the “lone wolf” provision. Under the “lone wolf” provision, a non-United States person who engages in international terrorism or activities in preparation for international terrorism is deemed to be an “agent of a foreign power” under FISA. To date, the “lone wolf” provision has never been used.

10. During calendar year 1980, the first full year FISA was in effect, the FISC issued 322 orders granting authority to the government for the requested electronic surveillances. In 2015, FISC approved collection activity in a total of 1,456 of the applications that included requests for authority to conduct electronic surveillance and 142 applications to access certain business records. The FBI also made 9,418 requests for information pertaining to 3,746 different United States persons; 31,863 requests for information concerning 2,053 different non-United States persons; and 7,361 requests for information concerning only subscriber information (e.g., name, address, telephone number) for 3,347 United States persons and non-United States persons.

Joe Carter is an adjunct professor of journalism at Patrick Henry College, an editor for several organizations, and the author of the NIV Lifehacks Bible.

Photo Credit: U.S. President Donald J. Trump and Former U.S. President Barack Obama exit the capitol to the east front steps for the departure ceremony during the 58th Presidential Inauguration in Washington, D.C., Jan. 20, 2017. DoD photo by U.S. Air Force Staff Sgt. Marianique Santos.