[Dave W]

They can’t do that. It is a federal law that all TV and radio stations must run any ad for federal office unaltered.

[Political Junkie Too]

Unaltered sure. But what if there is no ad time left to sell? I don't think there are any laws forcing a rationing of the available ad time. There are regulations for how much content time there must be each hour, so the available ad time is not infinite.

-PJ