"Voting for a third party accomplishes one thing. It takes votes away from one of the other major-party candidates. Given that the status quo favors the Republican candidate – think the Electoral College – voting for a third party is probably going to take votes away from Joe Biden. Whatever you think of him, he’s better than the alternative. (The alternative, by the way, likes making jokes about being a dictator.)
Actually, it accomplishes another thing. It enriches presidential candidates for third parties that do not work in cooperation with one of the major parties. (It’s called “fusion voting.”) For instance, the Green Party — these people know they can’t win. They know the status quo prevents them from winning. They don’t say that, though. In the space between what they know and what their supporters don’t know is a scam. In the absence of systemic change, third parties that don’t cooperate with one of the major parties are inherently exploitative."
It would reduce the problem significantly. If we had RCV back in 1992 I can see most of Ross Periot’s votes going to Bush senior as their 2nd or 3rd choice, winning him re-election.
Likewise I can see a lot of Greens votes in 2016 going to Clinton, with that being enough to give her the margin needed to win in the Electoral College.
Ranked voting still isn’t perfect in this regard, see for example: https://en.wikipedia.org/wiki/Ranked_voting#Defeat-dropping_Condorcet