Well, he didn’t just crawl out of a hole, he has a record. The article is making the claim that he has the potential to bring together different elements of the democratic party, which ultimately is the party of everyone else that isn’t voting Trump. This is a big tent with a lot of perspectives, and while democrats are largely united against Trump, that doesn’t inherently mean they’re just as united behind the candidate (as we just saw), and those kind of things are ripe for Republicans to pick at and promote infighting.