a) Biden, the Clintons, Pelosi, Schumer, Kerry, much of the MSM, etc. have been totalitarian communist traitors who want to destroy America for decades, possibly trained by commies during the Cold War era. However their plan was to wait until the time was right for Marxist revolution and otherwise wear the mask of a moderate politician. Their support for things like LGBT and environmentalism was always a long term play to get this point.
b) The Democrats 10-15 years ago were just normal stable moderates, still corrupt and warhawks, etc., but not commies. They genuinely believed in things like helping the environment and legalizing gay marriage. However they became part of the woke cult and underwent a psychological shift when the rest of the left did sometime in the last decade. As a result their brains have been hijacked at this point causing them to now be malicious totalitarian commies.
c, but closer to a)
They started as ethically challenged politicians and journalists, not communists, but were recognized as psycopaths (about 1% of men and 0.3% of women are), and slowly moved by their mentors from a more mainstream position in their younger years to a position now where they genuinely have lost all connection to humanity. They are now so poisoned that they no longer consider the rest of us to be the same species, and do not feel the slightest bit of remorse at causing us harm. Their support of Marxism, Fascism, or any other "ism", is merely one of convenience. They are happy to accept any system which guarantees them complete control. They have no ideology other than domination of us lesser beings for their own gluttony, and have always tried to increase their power at the maximum rate possible, using any community that is available to divide us. LGBT was merely a convenient tool that they stumbled upon as a divisive element along the way, and the environmental movement was hijacked because it was fit for purpose in terms of keeping the lesser human species at a controllable number and complete with science that could be easily obfuscated to support any position they required.