The voting system is designed to disallow 3rd parties.

Whatever 3rd party has to compete monetarily with the big 2 for ads and campaign funding. Already a crippling disadvantage.

Then, unless that 3rd party is exactly equally pulling votes from the big 2, it just ends up undercutting it's next best thing.

E.g. if a 3rd party ran and was mostly equally divided, but slightly closer to Dem than Rep...
It's still not big enough to win. So what's the result?
It siphons more votes from the party R or D that was closest to it, and the other side wins.


To the voter Dem who is considering voting for the 3rd party it's literally risking it all on a slim chance to make big change when the outcome is almost certainly that your 3rd choice wins. The safest bet is to vote for your #2 choice so that you don't lose by getting neither candidate you want.