The Republic did have the legal power to ban both of these organizations as early as 1922. The Republikschutzgesetz (Law for the Protection of the Republic) gave both the Land and central governments broad authority to suppress organizations deemed a threat to the Republic. These laws allowed for the temporary bans of media that encourage violence. Under the rubric of "endangering public safety," the Republikschutzgesetz outlawed the organizations from owning unauthorized weapons, the creation and brandishing of a weapons arsenal, and criminalized the failure to report on the existence of weapons arsenal. But gun control and regulation was not the primary focus of the Republikschutzgesetz but rather to restrict the operations of various anti-republican groups and provide grounds for their prosecution. The Republikschutzgesetz's provisions on firearms were predicated upon a pre-existing January 1919 Reichstag legislation which banned the private ownership of firearms to meet provisions of the Versailles Treaty which called for a wide-ranging German disarmament, including non-state affiliated militias.
The Law had a five-year life, but was extended in both 1927 and 1929. Inn the latter year, the Republic used the Republikschutzgesetz to ban the KPD's paramilitary wing, the Roter Frontkämpferbund (RFB). The ban was relatively ineffective; Berlin police reported that the RFB still collected dues and many RFB members simply did not wear their uniforms and insignia, but still hewed to their paramilitary organization. The ban restricted membership and new recruitment, but did not kill the organization.
Nonetheless, the ban of the RFB did send a clear signal as to the authorities' thoughts on Communist paramilitaries. But neither the NSDAP's SA or SS were banned in 1929, despite evidence of considerable violence by the NSDAP groups. Nor did the ban the Stahlhelm paramilitary of the right-wing DNVP or the socialist Reichsbanner Schwarz-Rot-Gold of the SDP. These paramilitaries continued to function in the chaos years of the Depression and their street brawls contributed to a larger sense of the Republic's terminal decline.
The nominal reason for not banning these organizations was that a group like the SA was only open to NSDAP members. Therefore, applying the Republikschutzgesetz to the SA or SS was not banning a paramilitary organization, but suppressing an internal part of a political party, which the Constitution forbid. But this type of rationale could have also applied to the RFB. The continued survival of both the Stahlhelm and the RSRG point to favortism on the part of the state towards those in power, but this still does not explain the reluctance to apply the law to the NSDAP, who were self-described political outsiders. There were repeated calls between 1930 and 1931 to ban the NSDAP's paramilitary wing, but the state and Land governments dragged their feet until April 1932 and the Brüning government banned the SA and SS.
But by this time, the SA, and to a lesser extent, the SS, had a large enough following to make the ban toothless. SA men simply wore insignia on the inside of their lapels or marched in plain white shirts. Various Land laws against uniforms were evaded through such measures. Moreover, both the SA and SS tended to frame their flaunting of the ban or ersatz uniforms as an issue of free speech protected by the constitution. The fall of the Brüning led to a reversal of the NSDAP ban by von Papen the following June.
This reluctance and von Papen's reversal showcases one of the fundamental problems of the Republikschutzgesetz: although the law itself was politically neutral, its application was not. Von Papen and his entourage certainly thought they could use the NSDAP for its own ends, but the reluctance to use the law against right-wing groups ran deeper than the immediate political milieu of 1932. The Weimar justice system, ranging from police to judges, was "blind in the right eye," meaning that right-wing radicals received far less attention for their activities than those on the left. Hitler and his fellow defendants' slap on the wrist for the Beer Hall Putsch was only one example of a justice system that was quite lenient for right-wing radicalism. In all the debates over applying the law to the NSDAP, few in the central government considered reversing the RFB ban. The various Weimar police departments investigated the KPD's groups with far more alacrity than equivalent right-wing opponents of the Republic.
This selective legal astigmatism did not prevent Hitler from making political hay from the few times the NSDAP felt state repression. Both in his run-up to power and after Hitler's appointment as Chancellor, the NSDAP would use these few examples of the Republikschutzgesetz as evidence that the NSDAP had triumphed against a hostile establishment that had stacked the odds against them. The Republic's use of political suppression became an opportunity for the NSDAP to cast democratic opponents of the Nazi seizure of power as hypocrites. When the Centre Württemberg State President, Eugen Bolz critiqued the NSDAP's antidemocratic moves in February 1933, Hitler responded in a speech attacking both Bolz and presenting his Chancellorship as a true defense of freedom:
Those who made no mention of our freedom for fourteen years have no right to talk about it today. As Chancellor I need only use one law for the protection of the national state, just as they made a law for the protection of the Republic back then, and then they would realize that not everything they called freedom was worthy of the name.
Bolz ended up forced out of office, spent a few weeks inside a concentration camp, and then in the political wilderness of the 1930s under Gestapo surveillance.
It is possible that Hitler and other NSDAP leaders may have believed that the main ire Republikschutzgesetz was directed at them. The NSDAP soon enacted their own version of Republikschutzgesetz in February 1933 as part of the Reichstag Fire Decrees, and Goebbels's diary entries from this period show a certain glee at meeting out vengeance and bans against their political enemies of the 1929-33 period. But the NSDAP's public rhetoric about the Republikschutzgesetz was half-right. The application of the law did stack the deck, but in favor of the NSDAP and their fellow-travelers on the right. They saw not only their ideological rivals on the left suppressed by the law, but could benefit from knowing how the RFB evaded it when the Republikschutzgesetz belatedly came for them.
Sources
Evans, Richard J. The Coming of the Third Reich. New York: Penguin Press, 2004.
Fulda, Bernhard. Press and Politics in the Weimar Republic. Oxford: Oxford University Press, 2009.
Swett, Pamela E. Neighbors and Enemies: The Culture of Radicalism in Berlin, 1929-1933. New York: Cambridge University Press, 2004.