Instant Runoff Voting" (IRV). A "First Past the post" voting system ends up either forcing a two-person presidential election or the complete disenfranchising of a third candidate.
The classic example of this is the 1992 Presidential election in which Clinton and George H.W. Bush were joined by independent candidate Ross Perot. Despite gaining nearly 20% of the vote, Perot won none of the electoral votes. Moreover the people who voted for Perot were probably likely to have voted for Bush, which means that Clinton won the election because the opposition vote was divided. This is a natural result of a "first past the post" electoral system, which is not very democratic.
Had IRV been the voting system in 1992, the chances are that Perot's votes would have ended up being given to George Bush (since Perot voters would have nominated Bush instead of Clinton as their second choice), and Bush would have won.
Another election that would've changed is the 2000 election - it could be argued that votes for Ralph Nader would have gone to Gore (since Nader voters would've nominated Gore over Bush as their second choice).
In the current climate, IRV would create a viable alternative to Trump, so that conservative voters who hate Trump won't have to vote Democrat or choose not vote at all. One of the reasons why Trump presents a crisis to conservatives at the moment is because of the First past the post electroal system./
In short, the Instant Runoff Voting system is a far more democratic voting system than the one currently used. Both parties would have benefited from it in the past had certain elections been under IRV, which means that both parties could choose to get behind the system and nominate its use in presidential elections with a constitutional amendment.