I would say a combination of already being rich, being old, and insider trading. Congress can't actually take personal funds from lobbyists legally.
Maybe if someone is in Congress, they can skirt the law around lobbyist gifts due to your position of power, but 1. it doesn't sound very plausible that someone becomes a multimillionaire by squirreling away illegal gifts or campaign funds and 2. to become I doubt small town city councils making these decisions are in a similar place. Most of reality is boring and not like the movies.