I hate to break this to you, but Bernie isn't a democrat. If you knew any of the history you'd know how tenuous his relationship is with the DNC, and how he isn't pulling any strings with anyone, quite the contrary. Just because you view anything to the left of authoritarianism as being democratic, that doesn't make it so.
The DNC enjoys Bernie's success because he pushes for many of the same issues and drums up support outside of the mainstream centrist democratic party, but ultimately he funnels his voters towards the Democratic nominee.
And as far as Harris being "radical"...ok sure. Move the goalposts all you want, but understand that she was by far the safe choice. There were plenty of options that would have been "Radical", but someone who was an attorney and then a senator is too spicy for you. Perhaps she should have been a reality TV star first to get more approval from the Republican party.
Overall it shouldn't matter if you have 3 separate but equal branches of government with functional checks and balances. The problem is you've consolidated all the power to the executive and the legislative branch has entirely abdicated their responsibilities. Fortunately it's shown us all the holes in our government we relied on good faith to not be exploited, but the real test will be if our democracy can adapt and strengthen itself or continue to be torn apart.