Well, yeah. Ads work. Americans don't spend half a trillion dollars per year on ghosts.
We like to tell ourselves that it doesn't work on us. It does. And the advertisers love that we think it doesn't work, because that means we're not noticing.
And I've got no idea what to do about it. The Supreme Court has been pretty clear that advertising is free speech. You need a fig leaf that you're not coordinating your ads with the campaign, but they barely enforce that.
There are limits to how much it can do. They wouldn't be spending $1B+ this time around if the first few hundred million had worked. They're trying to limit the damage, and even after the fact it'll be hard to tell how effective the spending was -- there is not control country to compare it to.
But note that this is a midterm, and even if the opposition party wins, they're going to be ineffective. Just wait two more years, and that $1.2 billion figure is going to look like petty cash.