Bernie Sanders' supporters are also a big problem.

For all the ways supporters of Bernie Sanders give him an immense strategic and moral advantage in the race, there are also some ways in which these supporters pose problems -- both for the candidate's electoral prospects, and for the success of the wider movement should he indeed be elected.

1. His supporters are angry, and this anger scares off many potential allies who think that although Trump and his ilk are monstrous, the basic corporate and civic reality doesn't need to be upended.
2. His supporters are often dogmatic, which is primarily a reflection of their moral and civic outrage at the injustices of modern America. But being dogmatic has a cost: it makes some potential supporters wonder whether the goal is to help as many people as possible or whether the goal is to take over the whole government and install a new orthodoxy. This "cost" is potentially worth it: Sanders has a movement and an ideology and the courage of his convictions, all of which are weaker in other candidates. But it's still a "cost" all the same: the dogmatic Sanders coalition may never include as much of the anti-Trump vote as it needs to. We simply don't know yet.
3. Some of his supporters are unkind. Sanders attracts some mean-spirited voters. So do all the other candidates, but Sanders' overall message is one of love, compassion, fairness and well-being. The nastiness of Sanders' supporters is used by other candidates to undermine that message, and it scares off many potential allies. How many? That's an important question.
4. Some of the supporters of Sanders are prone to believing conspiracy theories. They reject the anti-science views of the mainstream right -- and rightly so -- but engage at times in paranoid or strategically useless views. The gains in fervor that this results in may be outweighed by the number of people it puts off.