he's a guy that likes to throw mud at the wall and see what sticks. He always claims to have sources and insider info. on occasion he has been right. he was right on the money during the entire Brandon resigning deal. So I guess that gave him a bit of recent street cred.
I suspect that the reason that everyone is retweeting him is because they like what he's saying (i.e. harbaugh to michigan)
he's definitely not a complete hack but at the same time I personally don't put too much stock into what he says. just my opinion though.
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Sometimes people standing on third base think they hit a triple, but they didn't - Jim Harbaugh