They will. When primaries come, the Democratic party will soundly and democratically (little d) reject his attempt to represent them by not voting for him. Even before then, he will be rejected because nobody is going to give him the time of day when it comes to setting up a debate or using party resources to facilitate his campaign. Until then, he is not a representative of the party, just a dude who says he wants to represent the party. I could just as easily say I want to represent the Republican party by running a campaign on aborting every single fetus in the United States and then holding a giant gay orgy before forcing all cisgender people to undergo surgical transition. Obviously I would not be representative of the Republican party. Same with this guy and the Democratic party. The only reason it feels like this guy is in any way legitimate or affiliated with the Democratic party is because of how early primary/election coverage starts.