Trump's approval was 52/47 in the 2018 midterm exit polls in Georgia, unless he suffers some kind of approval rating collapse in 2020 relative to the 2018 midterms Trump will carry Georgia and Loeffler will win as a result, candidate quality doesn't really matter in a presidential year, its all going to be about how the presidential race goes in each state.
So, you say that Susan Collins will lose in 2020?
I think there's a pretty good chance she does if the Dems put up a good candidate, of course Maine is trending R pretty hard and Trump has a 50/50 shot at winning the state outright in which case Collins would win easily.