Gerrymandering doesn't affect the POTUS election, only House of Representatives voting. For POTUS, most states go by popular vote of the entire state with a winner-take-all of electoral college votes. Senate seats are also obviously winner-take-all.
The other stuff I agree with.
Apparently you don't understand how gerrymandering does work, how it effects the EC which does elect the POTUS, and how much more often the GOP has used it. Heard of Trump have ya?