He made the argument that if you support stand your ground then you would have to agree that Martin could have shot Zimmerman if had been armed because he feared for his life. That is a false argument because there is no evidence that Martin was scared, he could have made it to his father's house if he was truly scared and since he wasn't armed we it seems logical he would have done so if he feared for his life. There is also no evidence that Zimmerman every did anything worse than follow martin up to the point Martin started beating the crap out of him and bouncing his skull off the pavement. To argue the being followed is the same threat level has being straddled and beaten is beneath the office he holds and insults the intelligence of the American people (even if some dodge the insult by believing it is a valid argument).
His argument also supports the continued belief the Martin's race was a major factor in what happened despite the fact there is zero evidence to support that belief. When you believe something bad about someone based solely on their race and lacking any actual evidence isn't that almost the definition of racism?