Bernie seems more closer to the middle in terms of a lot of policies then Biden. Biden is an establishment democrat who seems more in for gun control, Obama health care, environment policies and so on. He is an absolute party canidate with little wiggle room. Bernie has the extreme health care and college policies, but that seems to be it. He takes more moderate stances on everything else. If I was to make a scale of establishment left to establishment right Trump and Bernie would likely be placed at the 50% marks between the middle and the end. That is why I believe the crossover between Bernie and Trump happens, both seem to be the closest to the middle for their respective parties, they just have those 1-2 policies that are on the far side