“Vote harder” don’t even start to work because US have a two party system with two right wing parties. Why there is no sign of a left party gaining traction? DSA is the biggest left organization but is miniscule (and not very left).
There is a way of radicalising, say… one tenth of the population?
Despite being Jacobin, this article does a decent job of describing the dirty tricks the two parties have used in the past to strangle upstart third parties https://jacobin.com/2016/11/bernie-sanders-democratic-labor-party-ackerman/
Tldr: capital control the electoral machinery and they won’t permit challengers.