I don’t think Hillary Clinton is unbeatable, and am not nearly as sure as some seem to be that she’ll be the nominee.
I think that it’s much more fluid and “up in the air” than it seems.
So, the Democrats are not unbeatable. I do think that is the narrative they’d like you to believe, though.
In January of 2008, nobody thought Barack Hussein Obama had a chance of that proverbial snowball of being elected.