Breitbart is a right wing news/opinion outlet that has been pro-Trump so far. One of their reporters, Michelle Fields, was attending a Trump rally. She went to ask Trump a question but someone allegedly grabbed her from behind and pulled her away violently leaving bruises on her arm. Initially the assault was caught on audio tape and another reporter (Ben Terris from the Washington Post) who witnessed the event was able to identify the assailant as Corey Lewandowski, Trump's campaign manager.

Lewandowski denied that he had grabbed Michelle and claimed they had never even met. He went on to publicly accuse Michelle of being "delusional" and making up the entire incident. Breitbart chose not to support their reporter but rather then swing all the way toward the conspiracy against Trump angle (which would make Breitbart by association look bad to Trump supporters) they had another Breitbart reporter create an article where it was revealed that a security guard and not Lewandowski who had pulled Michelle away, that Ben Terris was just mistaken. This alternative explanation was questioned as video tape clearly showed Ben Terris speaking with Lewandowski right after the incident, making a false identification seem harder to believe. The Breitbart opinion was further weakened when C-Span released footage from the time of the incident which captured the moment Lewandowski (and apparently not a security guard) was right behind Michelle and reaching for her arm before they where both obscured by the moving crowd.

The current situation is:

• Michelle Fields has filed assault charges which are being investigated by police. Police have not yet made an arrest.
• Michelle Fields, in light of her own employer trying to push her assault under the rug for political points, has resigned.
• Ben Shapiro, a well known right wing writer, speaker and editor at large for Breitbart, also resigned citing Breitbart's actions against Michelle.
• As of this morning Breitbart posted, then upon reaction tried to hide an article where they spun Shapiro's resignation as the actions of a left wing traitor, tying it into a grand conspiracy by 'left wing' site Buzzfeed to destroy Breitbart and did it using the writing name of Shapiro's deceased father David Shapiro.

Updates:

Kurt Bardella, Breitbart's spokesman, has resigned. In an interview with CNN he claims a narrative that Breitbart tentatively took Lewandowski's side when the facts where not clear but as the evidence has emerged against him Breitbart has actually harded its position against their own reporter rather then come to support her. He stated he could not be the public face for those actions and that Breitbart is lying about the situation.

Jordan Schachtel, Breitbart national security correspondent and a foreign policy analyst for a number of other conservative sites and think tanks has resigned. He told Politico "Breitbart News is no longer a journalistic enterprise, but instead, in my opinion, something an unaffiliated media Super PAC for the Trump campaign".

Joran Stepman, a Breitbart editor, resigned alongside Jordan Schachtel stating "Breitbart News has always been open about being grassroots, conservative publication, but in my opinion we are working with or perhaps even taking direction from a presidential campaign, which is unacceptable journalistic behavior. I believe Breitbart News is becoming less of a news site and more of a propaganda organization dedicated to the Trump campaign".

Regarding the original assault complaint the police have not completed their investigation. The Trump campaign and various media and social media supporters of Trump are advancing two arguments against the charges. The first follows Lewandowski's original claim that he never met Michelle and Michelle made up the entire incident to discredit the Trump campaign. This has been expanded into a list of accusations that she is a serial serial liar with a history of false assault claims that no one should trust Michelle's made up encounter with Lewandowski. The other argument they are simultaneously making is that Lewandowski barely touched her and it was only because he mistook her for an adversarial member of the mainstream media. This argument says that immediately after they had a nice talk where she had no complaint and that further she was in the wrong for walking with the group of other reporters and entirely invited Lewandowski to grab her but in a way that was totally not assault.

Someone also leaked slack logs from a Breitbart internal channel.