Why do liberals lie about the Bush family and their supposed link to Nazi Germany?

Lots of people did business with Germany in the 1930s. That didn't make them Nazis, and in fact Prescott Bush ended all trade with Germany when WW2 started. Liberals need some way to throw mud at their political enemies, however, and it says something that they have to lie to do it. It says they can't come up with any real mud.