In one instance we know where he found some of his information.
From the Daily Caller:
Washington Post columnist Dana Milbank appears to have asked the Democratic National Committee (DNC) to do the majority of the research for a negative column he wrote about Donald Trump in April 2016.Trump is running against Hillary Clinton, and Democratic Party, and the mainstream media.
Milbank's column was titled, “The Ten Plagues of Trump,” and featured a list of "outrageous things" said by Trump. One of the "plagues" listed by Milbank, for example, was "Blood" and centered around a quote from Trump about Megyn Kelly: "You could see there was blood coming out of her eyes, blood coming out of her wherever."
Internal DNC emails suggest Milbank's asked for — and then leaned heavily on — DNC opposition research on Trump for the article.
Yes, he's right. The system is rigged.