The last time a 3rd party got any significant portion of the vote was Ross Perot in '92 and '96, it had 0 significance.
https://en.m.wikipedia.org/wiki/1992_United_States_presidential_election
https://en.m.wikipedia.org/wiki/1996_United_States_presidential_election
18.91% in '92, 8.4% in '96.
Before that, you have to go back to '68 where a racist 3rd party won 13.5% of the vote, and the South, also had no significance beyond that election.
https://en.m.wikipedia.org/wiki/1968_United_States_presidential_election
LOL - Perot, and his charts, changed nothing. He became a punchline in '96 with his “Ok, I dropped out, no, wait, I’m still in.”
His supporters went on to Ron Paul, who was equally ineffective.