Popular with who? Health insurance he supports public option, which is popular with pretty much everyone except the most extreme progressives who are demanding "not optional, take it and like it." He supports universal background checks for gun purchases, which is popular with pretty much everyone, much to the NRA's dismay. He wants to address cliamte change, which is popular with everybody except the most extreme science denying dingbats. He supports a pathway to citizenship for the undocumented, which is popular with all the left and about half the right.
I'm not predicting he gets the nomination, I just wasn't dismissing him out of hand back when you wanted to, and I'm certainly not dismissing him now. The guy might be the next Bill Clinton, except Clinton's surprise victory that put him in the race was New Hampshire, not Iowa.