Now, they should be furious that they ever at one point thought they could trust Sean Hannity, but what he did Monday night really shook them to their core, according to Fox employees who have now spoken to other media outlets about it.
While Hannity has always been one of the president's staunchest supporters in the media and reportedly regularly advises Trump, it is unusual for any news personality to participate in a political rally. "They've done an incredible job for us", the president said, an apparent reference to Fox News.
Hannity and Pirro praised Trump - an avid supporter of Fox News - and encouraged the crowd to vote Republican on Tuesday.
Despite Fox's disavowal, the Trump campaign continued to list Hannity as a guest throughout Monday at the link where people could seek tickets to the event. But Monday night's rally crossed a new line, making explicit what had always been implicit.
The network is generally sympathetic to the Trump administration and a safe place for the president to have his views heard.
CNN on Tuesday reported that more than a dozen Fox News staffers said they were disappointed by Hannity's decision to participate in a campaign rally in Missouri on Monday night.
President Donald Trump looks at his watch near the end of a campaign rally Monday, Nov. 5, 2018, in Cape Girardeau, Mo.
Trump, who had appeared live on Hannity's show during a backstage conversation just moments before, summoned the Fox News host to the stage, and he obliged.
One Fox News employee described to CNN Business the scene at the NY headquarters of Fox News at the time, as a number of journalists inside the company's news division watched the episode unfold live.
Hannity defended his actions, claiming he was "surprised, yet honored" to be invited onstage and that the stunt was not planned. There is nothing real about what Fox News reports on any given day.More news: Apple Halts iPhone XR Supply Over Weak Demand
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It came after Hannity's prime-time show aired from the rally site. He described them as "livid". Is this your first day at Fox News and you didn't know what the network was? We have an extraordinary team of journalists helming our coverage tonight and we are extremely proud of their work.
Asked by CNN Business exactly how the matter had been addressed, the spokesperson declined to elaborate.
"Mia Love gave me no love and she lost", Trump said.
Hannity said on Tuesday that he was not referring to Fox News journalists when he made the comment. "They do fantastic work day in and day out in a fair and balanced way and It is an honor to work with such great professionals", he wrote.
Hannity has been rebuked by Fox in the past. He referred to the other reporters as "fake news".
On Tuesday, Hannity was back on Twitter denying that his onstage appearance in any way contradicted his earlier statement that he would not be onstage - because it was unplanned.
While Hannity has been able to get away with breaking normal protocol, the network had previously attempted to rein him in.
"Candidates who embraced our message of lower taxes, low regulation, low crime, strong borders and great judges excelled last night", said Trump.
Fox News canceled a planned Sean Hannity appearance at a Tea Party rally in Cincinnati in 2010. He was followed by another Fox News host, Jeanine Pirro, both of whom gave remarks from the lectern backing the president.