KATY TUR: [Stephen Bannon] rocketed to fame during the Tea Party wave, producing a documentary about Sarah Palin. Dubbed the most dangerous political operative in America, he is no friend to establishment Republicans or the RNC.

[...] 

Breitbart has pushed conspiracy theories about Clinton and has taken an outsized role bolstering Trump's campaign, often taking on Trump's battles. 

Previously: 

Breitbart News’ Worst Headlines

CNN's Stelter: With Trump Having Breitbart Executive On Campaign “We're Going To See The Most Fringy Ideas” “Bubble Up”

Trump Campaign’s New Chief Executive Is Roger Stone’s Huma Abedin Conspiracy Enabler

How Breitbart News Became The Official Propaganda Arm Of The Trump Campaign