He's likable as a personality, but he's not even particularly good on foreign policy, which is one area that leftists are usually clued in on.
>As the drumbeat for war with Iran got louder, Rep. Sanders voted for the Iran Freedom Support Act, which codified sanctions imposed since the fall of the Shah and handed out millions to “pro-freedom” groups seeking the overthrow of the Tehran regime. The Bush administration, you’ll recall, was running a regime change operation at that point which gave covert support to Jundullah, a terrorist group responsible for murdering scores of Iranian civilians.
http://original.antiwar.com/justin/2015/05/28/bernie-sanders-the-ron-paul-of-the-left/