Literally how could we do away with gerrymandering? It's bad and/or biased redistricting, right?
We could do something about the particulars of gerrymandering, but the thing itself is synonymous with democracy.
At large state elections would be far less biased. If you use a closed party-list proportional ticket for states with more than one representative. This would also open the way for smaller parties, effectively breaking the two party deadlock of current American politics. Such a system would force the major parties to cater to more moderate wings of their respective Parties, with more extreme members more likely to create a small splinter party with their own ticket.
This would probably handwave Trump as Hillary and Donald were nominated by the more extreme Left and Right sides of their parties. If the parties fell back under more moderate control neither would have won the Primary. Probably handwave quite a few presidents actually.
Hillary might have won in 08 as at the time she had more moderate support while Obama was the Left Wing favorite. McCaine had pretty broad support from the across the GOP so still would have been nominated. He would've likely lost to Hillary, just as soundly as to Obama coming off Bush years. Since the US electorate was heavily against any Republican candidate.
On the other hand he might have been president in 2000 since Bush was the Far Right candidate for the GOP and McCaine had more moderate support. Gore was supported by the more moderate Wing, which is why he picked Leiberman as his running mate. In a contest between the two McCaine was more likely to win over Gore than Bush by some polls during the primary.
If you institute such as system as far back as the 1800 it becomes impossible to predict the landscape of modern US politics. Since over such a long time those butterflies will have grown into Mothras.