General points

Firstly, a "common" attribute of many totalitarian states is that not all exercise of power is done within the legal parameters. Meaning, even if you have a functioning justice system, some state actions are essentially just taken outside it.

Another thing to keep in mind is the general development at the time in a more authoritarian direction. The demand of the first world war for a stronger state apparatus, in general, moved power in many countries from the legislative towards the executive, with delegation of powers. The extreme version of this is the state of emergency where even the constitution could be set aside.

The Weimar constitution, generally a part of the liberal constitutional tradition, had such an emergency clause in art. 48 § 2, where the measures didn't need the consent of the Reichstag. This was the article used by the Nazis to suspend several key protections of the Weimar constitution in the aftermath of the Reichtstag fire. My point here is to illustrate that some of the problems lie with the general trend of giving power to the executive at the time and the prevailing trends, not just the Nazis in themselves. The Nazis got in power to a large degree by (ab)using the existing system. It's worth noting that art. 48 § 2 was extensively used before the Nazis as well, a book of mine explains it as "at times seeming like a permanent state of emergency".

To quote a famous Nazi Jurist, Carl Schmitt (1888-1985), on state of emergency powers: "Sovereign is he who decides on the exception".

On the changes by the Nazi regime

The Nazis when they came to power in 1933 did not formally remove the Weimar Constitution, but they approved a lot of delegation powers that in reality neutralised the separation of powers, democratic basis and rights chapters of it. The Ermächtigungsgesetz of 23. Marc 1933 transferred legislative powers to the executive for four years, but was renewed in 1937, 39 and 1943. They also, famously, established the nazi parti as the state party and made other parties illegal.

The key legal thing to note about the Nazi takeover is that it largely was a gradual executive takeover of the legislative branch. It was thus not a fundamental break with the earlier system, there is no clear date of any revolution, or even of something fundamental happening. There was never a Nazi constitution, just a bunch of delegated powers and singular decisions or simlpe laws, and of course non-legal means of upholding power. This is exemplified by the Nazis continuing a lot of pre-Nazi plans, like the establishment of the Supreme administrative court in 1941.

This has been dubbed a "dual state" where there were tensions between the surviving "normal state" and the constant state of emergency and constant interventions and abuse, both legal and non-legal, from the state. During the war, the remains of the "normal state" for the most part broke down completely.

All of these changes happened without any noteworthy resistance from the established state organs, especially the judiciary, but also without too many changes to it. That's why i describe it as primarily an executive takeover of the legislative and a "double state". Even in a speech as late as May 23 1942 Hitler affirmed that he did not want the party to interfere in the functioning of the judiciary.

Continued below