I think it indication of a section of voters. Add on the ones who will vote down ballot only, and stay home, and there are real problems ahead for Biden.
I also weigh in the ones who, like the Trump voters who admitted after lying to pollsters, may not be revealing real intentions.
Are these hard numbers? Obviously not.
But in 2012 a little over two million voted third party. In 2016 over 7 million. With the Dem numbers remaining flat and the GOP up 3 million.
I'm thinking a pattern is emerging.
I know you do. But that is a very short trend line. The last time voters moved enough to third party to have the winner of the popular vote lose the electoral, the next election saw a massive move away from third party.
Your trend line falls apart the moment you put George W Bush back in. You have picked the DEM highest point - 2008 - which almost everyone agrees wasn't just a surge of support for Obama but a massive rejection of Bush and the GOP after their colossal fuck up and decided that the reversion back down there is due to the loss of progressives, and not the loss of people who normally would have voted GOP going back home.
The theory that "progressives" are moving third party isn't outrageous, but it also competes with the theory that "white men" (especially non-college educated) are moving to the party of white identity and that there is just a general return to the mean of votes after the "fuck the GOP" moment of 2008.
I don't know the answer. But so far the "it is progressives fleeing" doesn't look very strong. Sanders's support went down. His theory that the non voters would be mobilized never happened. The 2018 midterms saw huge gains with suburban moderates and not a lot of progressive candidates win. Third party voting in the midterms wasn't significant.
There is also the question of the Libertarian vote vastly outperforming the Green. That implies that the third party/disaffected vote isn't particularly progressive but is more just generalized "anti-establishment" or simply right wing but rejecting culture war religious issues or outright white supremacy.
We will see. Maybe you will be right and there will be an even stronger shift to third parties this year. I remain skeptical.