A situation like this could only happen in the US if A) our country started to have really serious problems and B) there was a group that we could scapegoat for those problems.
If I had to make up a scenario in which this could happen, I would envision us losing economic and political power to China and to the forces of globalization (and through the ineptitude of our own political leaders). In such a case, we might start looking to persecute scapegoats. It's harder to find who we would scapegoat, though. My main thought is that it might be Hispanic immigrants. The major problem with envisioning that is that there are so many Hispanics who are not immigrants and who would protest vigorously if we started moving too strongly against the immigrants. However, I don't think there is any other group that might be scapegoated right now.
The 1940's was the combination of several military dictatorships throughout Europe, not just Germany but also Russia (and other countries). Germany and Russia embraced two political views at their extremes: extreme right-wing conservative and extreme left-wing liberal. Both clashed and produced genocides across Europe. We need to remember that the Russian Communists commited grave crimes against humanity during the 1940's and 1950's. Many innocent civilians (Orthodox Christian for the most part) were taken away from their homes to die as war prisoners in Siberia. And this is just one example of genocide during the 1940's.
So, to answer the question above, I would say it would happen only if there would be strong military dictatorships around the world clashing with each other in unscrupulous ways.