Bit of a rant here, so TLDR:
Ranked choice voting would make the biggest step towards fixing our current state of political affairs and would likely bring about the end of the "two party system" that, statistically, the vast majority of Americans dislike (actual Democrats and Republicans only make up about 25-30% of the US population)
Tbh, the whole "first past the post" election style that has lead to the 2 party system we have is the biggest reason why American Politics is so FUBAR atm.
As it is, both Republicans and Democrats are largely disliked by the VAST majority of the US. So how do they keep getting elected? Fear. Progressives fear what will happen if the republicans take power, so they vote democrat, and the conservatives fear what will happen if democrats are elected, so they vote Republican. In the end, we're all voting for the one we think is the lesser of two evils.
As such, Democrats and Republicans alike don't have to put that much effort in to having strong policies, they just have to have policies that appeal to more people than the other guy.
How do we fix it?
Instant Runoff/ranked choice voting. You get to vote for any/all the candidates you like, and none of the ones you don't, in order of favorite to least favorite. Once all votes are in, the one with the least votes gets eliminated, and everyone who voted for them has their ballots shift to their second choice. Then they eliminate the new person with the lowest votes, and all of their votes go to the 2nd or 3rd pick, rinse repeat until there is one candidate who has the most votes.
This would all but eliminate attack ads (which I have yet to hear anyone say they like), because when you have more competition, it becomes more about running on your own solid platform rather than trying to shake your opponents. A single opponent is an easy target, but 6 or more opponents becomes much more difficult to slander, so rather than taking other candidates down in ads, they need to focus more on building themselves up.
It would also help curb gerrymandering, as when you're trying to get specific percentages of voters, it's significantly harder to lump demographics when there are 5/6/7/8 potential candidates the voters could be voting for.
It would break us of the headlock the two party system has us in and would incentivize disenfranchised voters to actually turn out and vote. As it is, we will never see a libertarian, a green party, or any other "3rd party" candidate win the election because people would rather use their one vote to vote for the 2nd worst option rather than the best option, because 2nd worst is still better than the worst.