Employer retailiated my responding to a performance memo by terminating my employment.

Do I have good grounds for a "retaliation" lawsuit based on the following information.

My immediate supervisor prepared a "Improvement Plan" memo that contained several issues that were used as the basis for saying that I was a poor performer. I responded to that memo with the facts as they really were and, in that response memo asked if I was being singled out as "not being a good fit" (his term that was not defined)in the department because of my age of 57, and/or a hispanic vietnam veteran. He became enraged, excluded me from many of the activities taking place in the office, did not provide leads for new business as he did my associates, increased my performance
goals,and subsequently terminated my employment with no severance pay, even though some of my associates were separated from the company and given 1 year salary and medical. I was not even given the opportunity to resign.

Prior to my 6 months with this department I had received excellent performance reviews and received the highest bonus allowed. I worked for this company for 3 years prior to being assigned to this department.