Washington (CNN) - Before Donald Trump and Steve Bannon were enemies, they were allies. And not long before that, Bannon was part of an effort to sink Trump's presidential hopes -- even if Trump didn't know it.

A conservative watchdog group led by Bannon tried to discredit Trump in the early stages of the 2016 Republican presidential primary by shopping a document alleging that Trump had ties to mobsters, according to conservative sources and a copy of the document reviewed by CNN.