The answer is threats to civil liberties.
The Sacco and Vanzetti case consisted of two Italian anarchists being executed for a crime they most likely did not commit. The evidence for the case does not definitively prove that these men committed this crime. However, due to their radical political views, it was easier for American citizens to convict them.
The Red Scare was a time period in which the American government searched for suspected communists by violating rights guaranteed in the US Constitution. A perfect example would be the Palmer Raids. Attorney General Mitchell Palmer ordered the raid of 6,000 homes of individuals who were suspected communists. However he did this with no warrants or no evidence to support his actions.
Lastly, the KKK used violence and intimidation to hurt African-Americans. Along with this, they also used these tactics to ensure that African-Americans did not use their freedom of speech or their ability to vote.