realreferendum.org

https://www.ncsl.org/elections-and-campaigns/initiative-and-referendum-processes

https://lawreview.law.miami.edu/national-referendums-federal-constitutional-legislative-issues-public-direct-say/

https://www.reddit.com/r/explainlikeimfive/comments/1erq7og/eli5_why_doesnt_the_us_have_federal_level/