He can influence campaigns and election results. He can open channels to most powerful people and have his words heard. If no leader bends to their will, it is still far more influence than what you and I have.

Politicians invest whole careers and lives to play the game of politics. They gain power but not much wiggle room, too much is at stake to keep them in positions. Rich people on the other hand can buy the ticket to sit at the table, and they can leave any time they get bored. Having that kind of power without inherent responsibility is dangerous.