The origin of this astonishing, absurd and dangerous allegation appears to be the conspiracy site Infowars, run by Alex Jones.
Faking a Mandate
Michael Arnovitz
44061

According to Trump’s spokesman, his source was the Washington Post (specifically an affiliated blog called the Monkey Cage). Not sure when the preceding note was added, but here it is:

https://www.washingtonpost.com/news/monkey-cage/wp/2014/10/24/could-non-citizens-decide-the-november-election/

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