Reasoning: Politicians that receive large donations end up controlled by donors and therefore, they serve the donors and not their constituency.

Separating money from state is key to solve this problem.

How do we solve this?

The only individuals in any "democratic" government across the world able to separate money from state are the law makers, which, by design, are the ones with the most donors, therefore, the chances that they will create laws with the intention to separate money from state are, IMO, zero.

A potential solution is a complete dissolution of government followed by a presidential executive order that makes it illegal for any law maker or politician to receive any donation making the allocation of money for political campaigns, for instance, to be funded by the state from corporate taxes collected and distributed equally among candidates. That would, IMO, be more "democratic"