Political ads are not designed for targetting unpersuadables. Over the very long term propaganda that over and over blames undocumented people for problems starts to take a toll which could pull someone out of the unpersuadable demographic. But to a great extent they influence pursuadable voters in swing regions.
You say you would not switch to voting for Trump, and yet the sole reason Trump took power in 2016 was precisely due to advertising. Read about Cambridge Analytica and Peter Thiel. If Peter Thiel had not introduced Cambridge Analytica to the Trump campaign and bought Facebook data, Trump would not have taken power in 2016. THAT is how important advertising is. C/A master-minded indentifying the most important pursuadables, did a deep analysis of exactly what issues would be of interest to those individuals, and targeted them surreptitiously.
I strongly recommend you watch the PBS series “Hacking your Mind”. This episode in particular:
This thread is relevant:
slrpnk.net/post/14944065