If you are an at will employee, targeting you to be the next one terminated is perfectly legal as long as the reason for the targeting is not due to discrimination. Remember that in order to file a discrimination complaint, you must be able to show a legal discrimination basis such as age, sex, race, color, religion, disability, retaliation, or another one that your state has specified.
You may want to start keeping track of what the supervisor says, the date, the time, witnesses, and what happened. If you are being discriminated against, this record may be able to help you prove your case. This is especially true when your supervisor is verbally abusing an employee and says things that are discriminatory. By consistently writing down what happens at the time of the incident, you are keeping a record that the courts will recognize, almost like an audio recording.
Finally, you may want to speak with a local employment attorney about your rights as an employee in your state. Many states have laws that give employees additional rights that we have not reviewed in this book.