The Sanders campaign has combined what ought to be mainstream liberalism and rhetorical radicalism. Consider—you don’t have to go all the way to Denmark; Canada already has single payer healthcare and free higher education. This is not a program from out in the ozone somewhere; it’s perfectly normal welfare state capitalism. He dresses it up, however, in language about revolution and upheaval, even using the daring s-word. This has shown a lot of appeal to young voters but may also intimidate others who might support him, and it would probably be a handicap in a general election against a truly radical, destabilizing Republican. You would want to call attention to the risk posed by a Trump or a Cruz by presenting yourself as a safer choice.
Why not do it the other way around? Push the policies further to the left by proposing changes to corporate governance and more far-reaching reform of labor law (for instance), while speaking in soothing language about “updating” the economy, improving performance, evidence-based approaches, etc.? I think the more ideologically attuned portion of his base would value stronger substance, while the less fire-breathing posture (sorry about the mixed metaphor) would assuage the worries of those less inclined to take a giant leap.
I realize it’s way too late for this, and it goes against Bernie’s personality type, but perhaps it can be given more thought next time around.