Sanders is in denial right now. He's a regional candidate for the most part. Northeast with some pockets in the Midwest maybe.
Well what the Sanders Campaign is looking at (and I'm copying this from Robert Reich, who's a big time Bernie supporter)
"1. In the next few months the primary map starts tilting in Bernie’s favor: In later March: Maine, Michigan, Florida, Ohio, Illinois, Arizona, Washington state, and Hawaii. In April: Wisconsin, New York, Connecticut, Maryland, Pennsylvania, Rhode Island. In May: Indiana and Oregon. In June, California, New Jersey, and New Mexico."
Keep in mind, there's basically no evidence that he has a prayer in some of those states. I have no clue what polls Reich is looking at that thinks Bernie can win New York, Florida, or Ohio. As all polls from them I've seen have Hillary comfortably in the lead. I think Reich forgets that while NY is a very solid blue state. It's wall street blue. He would be hard pressed to beat Hillary on her home court.