They're not endorsing candidates in exchange for money. They do use their money to run their networks, which they use to promote certain candidates and positions.
Re: "The line is clear: is money being exchanged in order to promote a product? That's advertising."
There would be a chilling effect on speech. People would be afraid to speak or be imprisoned for saying the wrong things. North Korea is the only country that bans advertising.
Re: "The line is clear: is money being exchanged in order to promote a product? That's advertising."