Do i have a case against my company?

I am a co-manager at restaurant in florida, and the owner of the company iI work for tried to make me quit after I told him I didn't believe that he gave an employee that I saw doing drugs on the job a drug test. I was told to quit or i would be demoted at a 3 dollar a hour pay cut because, in his words, I called him a lie which i never said, and he was offended. The owner asked me if I thought he gave the employee a drug test so I told him that I'd seen the employee doing drug and I didn't believe that he could p a drug test. When i refused to quit, my employer started screaming at the top of his lungs at me and putting his fingers in my face as if he was going to hit me. I was then written up the next week for cussing out another manager which I didn't do. However, I did sign the write up because I couldn't risk losing a weeks pay. This happen about a month ago and ever time I go to work I am miserable, physically sick and emotionally drained. What should i do now.