politicians in the US derive their power from their ability to raise money from rich donors, while rich donors derive their power directly from their money

Technically they derive their power from the electoral mandate, but to achieve it requires a lot of money from said rich donors - so they don’t derive their power from it, it’s more a prerequisite to play at all. The second half is true. The rich are just rich, nobody voted them into wealth, that’s why they’re more powerful than the politicians.