Answer:
Ad Hominem
Step-by-step explanation:
Ad Hominem is an error in reasoning wherein, the character of the arguer is attacked instead of focusing on the argument at hand. This fallacy can be found in the communication between the two individuals in the question above.
Instead of focusing on the argument in question, Person B decided to attack the character of the first arguer by calling him an America-hating liberal. This attack might be relevant or irrelevant to the argument.