https://ballotpedia.org/Ballot_access_for_major_and_minor_party_candidates
Check out this, they got a neat table of the last time every state had a third party gubernatorial candidate crack 5%.
It has at least one error though, it lists the last time it happened in Maryland as being the victorious Know-Nothing in 1857 (which would be the longest). I immediately recalled that in 1966 a liberal indie did better than 5% against Agnew and the Segregationist rat, almost 10%.
But off-year races can be more educational and clean.
One thing I like about Trump’s ‘dirty’ tactics is that they are often shorthand for the truth. Awsome how he does that.