:The Imperial Presidency" is a book by Arthur M. Schlesinger, Jr., a book that he wrote in 1973 in response to Richard Nixon's presidency. He chronicled the history of US Presidents doing stuff on their own without bothering to seek Congress's approval, and RN gave him a lot to write about.
Claiming emergency powers is dangerous, because that sort of thing can be used to take over in Julius Caesar fashion.
Reichstag fire: On 27 February 1933, a fire started in the German Reichstag building, its parliament building. The authorities found a Communist anarchist, Marinus van der Lubbe, who tried to start a fire there, but another theory is that Nazi leaders started it and that MvdL's presence there was pure luck.
When someone phoned Nazi leader Josef Goebbels about the fire, he dismissed it as a "tall tale", and he only reported it to Adolf Hitler the second time. Nazi leader Hermann Göring said about it "This is Communist outrage! One of the Communist culprits has been arrested." Hitler considered it a "sign from God" that the Communists were starting a revolt. German news services stated about the fire that "this act of incendiarism is the most monstrous act of terrorism carried out by Bolshevism in Germany" and "the government is of the opinion that the situation is such that a danger to the state and nation existed and still exists".
The day after the fire, at Hitler's request, President Hindenburg signed the Reichstag Fire Decree into law by using Article 48 of the Weimar Constitution. The Reichstag Fire Decree suspended most civil liberties in Germany, including habeas corpus, freedom of expression, freedom of the press, the right of free association and public assembly, the secrecy of the post and telephone.
The German authorities then outlawed the Communist party, arresting many of its members, because of this fire.
This helped the Nazis in the parliamentary election soon after. This led to the Enabling Act, a law which gave Adolf Hitler the right to rule by decree without consulting the Reichstag. It was passed a few months later. Over the coming months, Hitler and his henchmen consolidated their power, outlawing other political parties and carrying out a purge of the SA "Brownshirts" militia that had supported them in their rise to ower.