doesn't each party pay for their own ads? or are they all sponsored by other groups?
the parties arent part of the government per se, they're essentially just lobbyist groups that run on donations and is for all intents and purpose, a private organization.
if you ever take a look at american politics it gets really, really weird. a lot of times you'll see ads on tv ads sponsored by "The US Chamber of Commerce," which turns out has no ties to the government and is just a lobbyist group for fortune 500 companies.