A constitutional dictatorship is a form of government in which dictatorial powers are exercised during an emergency. The dictator is not absolute and the dictator's authority remains limited by the constitution.
The Roman Republic made provision for a dictator who could govern unchecked for a stipulated period of time. Unlike other magistrates, a dictator was not subject to review of his actions at the conclusion of his term.
The United States Constitution has a similar dictator clause stating that the President "may adjourn [congress] to such Time as he shall think proper" if the two houses disagree on when to adjourn. Abraham Lincoln, President of the United States during the American Civil War, exercised extraordinary powers to preserve the Union. Lincoln's dictatorial actions included directly ordering the arrest and detention of dissenters and the suspension of the right to writs of habeas corpus. However, Lincoln remained subject to Congressional oversight, judicial review, and periodic elections.
The Weimar Republic, which succeeded Imperial Germany after the First World War, adopted a constitutional provision that expressly enabled the president to rule by decree, without consultation with the legislative branch. That provision was used by Chancellor Hitler to consolidate his powers upon his selection by President Hindenburg.
US President Franklin D. Roosevelt also exercised extraordinary powers in response to the Great Depression and the Second World War. Roosevelt's actions included violating the US Constitution's Contract Clause, the closing of banks, and a moratorium on foreclosures. Later, meeting a perceived threat by Japanese nationals and Japanese-Americans, Roosevelt ordered their relocation to internment camps.
In the 21st century, John Yoo, attorney and legal theorist, has offered a theory of the unitary executive for massive authority of the US President, in his capacity as commander-in-chief of the armed forces. Yoo provided the intellectual foundation for many of the actions undertaken by the George W. Bush administration in the aftermath of the attacks of September 11, 2001.