Article I, Section 9 of the Constitution establishes strict exceptions to the right of habeas corpus, the centuries-old legal tool that allows prisoners to challenge their detention in court. The Suspension Clause states that habeas corpus can only be suspended "when in Cases of Rebellion or Invasion the public Safety may require it," limiting government power to deny this fundamental protection.
President Abraham Lincoln suspended habeas corpus during the Civil War, and Congress did so again in 1871 in nine South Carolina counties to combat the Ku Klux Klan. These rare suspensions highlight the framers'' intent to protect habeas corpus except in the most extreme threats to national security. The Suspension Clause protects the writ as it existed in 1789, when its core function was reviewing the legality of executive detention. Modern courts have held that restrictions on successive habeas petitions do not amount to unconstitutional suspension, provided they aim to prevent abuse of the writ rather than eliminate access to it entirely.