Because Democrats are dealing with someone that doesn't fit their mold. He's a product of their policies and philosophy but doesn't walk the party line. Meanwhile mainstream Conservatives are making up reasons for why they are so upset that a super liberal city elected a super liberal which should be expected. The reality is they are dancing around the fact that he's not submissive to the Israel lobby and that makes them freak out. He's liberal sure but he's a liberal that's not going to be kissing a wall anytime soon.