Who exactly is he "uniting"? The young, ignorant and excitable led by an ossified relic of a morally and intellectually corrupt ideology? - not exactly an inspiring picture of national unity.
I understand his appeal, on the purely emotional level, if the alternative is the Robot-Lizard Lady, or Trump. At least you have a human being.
But of course he is a populist divider, just like Trump.
His villains are "corporations at large" rather than "corporations that hire illegals and trade with the Chinese" - in other words, the same "blame "them" and "trust me (endowed with the crushing power of the State, please) to fix it". "It" being the undifferentiated mass of problems, real and imaginary, neither candidate is remotely qualified to understand, let alone fix.
As Mr. Mencken said, "The central belief of every moron is that he is the victim of a mysterious conspiracy against his common rights and true deserts".
Trump and Sanders are natural leaders of those morons - slightly different flavors, marketed to different demographic groups.