To what extent did the rise of the Nazi party and the introduction of Nazi policies in the the 1930s influence expressionism and the arts in Germany?

The Nazis rose to power in part from backlash over the shock of the new: not only did the Germans experience the jolt of their first-ever republic after having been ruled by princes for thousands of years, but during the period of the Weimar Republic, all sorts of artistic experimentation flourished, especially in big cities like Berlin.
After he became chancellor in 1933, Hitler banned all art he labeled "decadent," which included abstract, non-representative art, as well as forms of modern art like expressionism. Hitler, who himself painted and who had attempted to get admitted to art school, decreed that all art must be representational and follow traditional forms.
The 1933 Enabling Act gave Hitler the legal power to impose his views on German artists. He established a Chamber of Culture under the direction of Joseph Goebbels. This organization imposed strict censorship on the arts. To be able to work, visual artists had to join the Reich Chamber of Visual Arts, which monitored their work to make sure it adhered to the vision and aesthetics required by the state.
As a result of theses policies and Hitler's harsh rhetoric against modern art and artists, many artists left Germany after 1933. Those who remained were likely to paint heroic depictions of the German Volk or nineteenth-century style landscapes featuring horses and idealized settings. Nazi policies, in short, had a stifling effect on artistic expression, favoring conformity over creativity.