Powers like these have been deployed sparingly: A few days after the Sept. 11 attacks, a proclamation declaring a national emergency, followed by an executive order days later, invoked some presidential powers, including the use of National Guard and U.S. military forces.

What little we know about these secret powers comes from the Brennan Center for Justice at the New York University Law School, but we believe they may include suspension of habeas corpus, surveillance, home intrusion, arrest without a judicial warrant, collective if not mass arrests and more; some could violate constitutional protections.