Corporations, in America, where the travesty known as Citizens United exists.

(I'm not claiming that other countries don't have money in politics; but America is the one where it is most clearly enshrined with an actual name to the philosophy)

Incumbents, of course. The ones holding the largest interest in preserving the status-quo and freezing competition. Professional organizations needing power to preserve the barrier of entry. Huge, trans-national Unions.

But other power brokers as well. Other politicians with more money. Their own stock holdings. Foreign powers. Well moneyed interest groups. Ideological organizations siphoning old money.

Occasionally even the scrappy start-up trying to game the system. These usually fail, see SBF - but they are not saints either.

There is no shortage in interests vying to corrupt politicians. Somehow they never mind and always succumb.