or NSDAP. In a sign of the crisis, Severing returned as Minister of the Interior in October 1930. He named his predecessor Albert Grzesinski as Berlin's chief of police. Braun, Severing and chairman of the SPD parliamentary group Ernst Heilmann supported the SPD's course of tolerating Brüning due to the lack of political alternatives. The National Socialists saw Prussia as an important strategic target in taking over power in Germany. Joseph Goebbels wrote in 1930, "The key to power in Germany lies in Prussia. Whoever has Prussia also has the Reich." Others on the right saw the situation similarly. Unlike during the Reich government of Hermann Müller (28 June 1928 – 27 March 1930), Brüning temporarily blocked cooperation with Prussia against the NSDAP. In December 1931 the Reich government prevented the execution of an arrest warrant against Adolf Hitler issued by Berlin police chief Grzesinski. The Prussian government then presented the Reich government with an extensive dossier proving the anti-constitutional activities of the NSDAP and announced a ban on the Sturmabteilung (SA) in Prussia. Only after such pressure did Brüning also support the ban of all paramilitary units of the NSDAP at the Reich level. Referendum on the dissolution of the state Parliament In 1929 the Braun government banned the paramilitary Stahlhelm in the Rhineland and Westphalia for violating the demilitarization provisions of the Treaty of Versailles. In 1930, when the Young Plan on German reparations came into force and foreign troops were to evacuate the Rhineland, Reich President Paul von Hindenburg, who was an honorary member of the Stahlhelm, forced the ban to be lifted by threatening not to take part in the celebrations in Koblenz to mark the evacuation. At the end of May 1931, Stahlhelm leader Franz Seldte sharply attacked the "Marxist" Prussian government at the Reich Front-Line Soldiers' Day in Breslau. He announced a plan to call a referendum for the premature dissolution of the Prussian Parliament. The Stahlhelm's move was supported by the DVP, DNVP and NSDAP, and 5.96 million Prussians signed the initiative to put the referendum on the ballot. This was slightly more than the necessary 20% of eligible voters, and the referendum was held on 8 August 1931. Under pressure from Joseph Stalin and the Comintern, which at the time considered the fight against the "social-fascist" SPD more important than resistance to the extreme right, the KPD also supported the referendum. Especially