After the failed Putsch of 1923, Hitler went to prison for 9 months. He could have been deported and barred from Germany *after* a five year prison sentence. But the government treated him with kid gloves.
/
How did Hitler transform the tiny Nazi gang and Friekorps into power?

After leaving Landsberg prison in 1925, Hitler made a conscious decision, which he enforced in the Party, to seek power through the electoral process. While Nazi thugs still murdered people, they did it under the direct control of Hitler and Goering. It became part of 'strategy.'

The other part of the strategy was 'legitimization.' The public face of the Nazi party became lawful, in a manner of speaking. Rules imposed by local regulations, such as the banning of Nazi uniforms in one province, were followed by the Nazis themselves.

Over time, these efforts by Hitler gave the Nazis the appearance of respect for the rule of law and the parliamentary system. Of course, the repugnant nature of Nazi ideas limited their electoral success to a tiny number of elected parliamentarians. Until the Great Depression.

That event caused massive social dislocation, throwing about half of the German workforce out of their jobs. Nazi representation in the Reichstag grew, but they never attained a majority, and Hitler himself, of course, was never elected to anything.

The Nazis did, however, have rough parity with the other major party in Germany at the time: The Social Democrats. This party was an anathema to many capitalists and President Hindenburg - and it wasn't long before they decided to use Hitler to suppress labor and the SDs.

The rest, as they say, is history.
/
The key point is this: Assuming power isn't a matter of flashmobs taking over government buildings. It's a matter of building a social movement which has more than just sympathy, but real economic and political power. Hitler understood that.