We know this. Reagan knew this when he opened the door for lobbyists.
According to Marx ( Das Kapital ) corruption of the government towards the interest of the owning class is inevitable.
We still don’t know an effective way to keep government public serving. Marx recommends the end of hierarchy, but that model needs some development.
But yes, government is intended to serve the public and when it doesn’t (such as with regulatory capture) that is government failure. US federal and state governments typically fail, only rarely enacting policy consistent with public interest.