Max Weber argues that there are two types of politicians.
- Those that live for it
- Those that live from it.
If you're living for politics, and focussed completely on that, it's necessary that you are independent and available, meaning you should have enough money to live and the earning of that money should not require you to be physically involved. Examples would be rentiers, be they feudal lords or landlords of today. This basically means that you need to be a part of the plutocrats, who generally will not have incentives to change the current system too much.
Otherwise, if you're living "from" politics, meaning you, as a professional politician, depend on it for your income, you either take bribes for services (illegal) or play power games inside the party to get the ability to allocate party capital.