20% is 1/5. It is still too much but not the end. 80% did not vote for them. And the left go stronger too and keeps growing. This is the beginn of the fight, not the end.
We are on it. There are several efforts, including high-profile ones, to ban the AfD. At the same time, we are fighting fascism on all fronts, online and offline.
“Extremes” both sides, ie. the Nazis and the Left party, are more popular in the east, no doubt because it is poorer, so people are less satisfied with the status quo.