The war of words between Donald Trump and Fox News turned nasty Wednesday night.

On Megyn Kelly's Fox News talk show, conservative columnist Rich Lowry asserted that Carly Fiorina had castrated Trump during the CNN debate last week.

Lowry, a prominent Trump critic, referred to Trump's private parts and said Fiorina had the "precision of a surgeon."

Kelly, who looked shocked at the remark, said "what did you just say?"

Trump was apparently shocked too -- he lambasted Lowry via Twitter, calling him "incompetent" and adding, "He should not be allowed on TV and the FCC should fine him!"

The FCC -- Federal Communications Commission -- occasionally fines broadcast networks for indecency, but has no power to sanction cable channels like Fox News.

Lowry gleefully replied to Trump on Twitter: "Man, you can dish it out but you REALLY, REALLY can't take it."

Fox News had no immediate comment on the off-color moment.

>> Thursday morning update: here's what Trump said about Lowry on CNN's "New Day"

For the time being, Trump and Fox are at loggerheads, and Wednesday's back-and-forth about Trump's anatomy isn't likely to change that.

The conflict began heating up again around noon on Wednesday, when Trump tweeted that he would be boycotting Fox because the network has treated him "very unfairly."

"I have therefore decided that I won't be doing any more Fox shows for the foreseeable future," he wrote.

But a Fox News spokesperson suggested Trump wasn't telling the full story. In a statement to CNN, Fox said "at 11:45 a.m. today, we canceled Donald Trump's scheduled appearance on 'The O'Reilly Factor' on Thursday, which resulted in Mr. Trump's subsequent tweet about his 'boycott' of Fox News."

Fox News declined to specify why it had canceled Trump's appearance. But the decision came after a series of tweets Trump posted on Monday and Tuesday criticizing Kelly's and Bill O'Reilly's shows, sometimes in highly personal ways.

"Enough's enough" is how one Fox source put it on Wednesday.

A second source argued that Trump was antagonizing Fox to create controversy and draw attention to himself at a time when other candidates are surging in the polls.

"When coverage doesn't go his way, he engages in personal attacks on our anchors and hosts, which has grown stale and tiresome," the Fox News spokesperson said. "He doesn't seem to grasp that candidates telling journalists what to ask is not how the media works in this country."

Fox also criticized the media for its initial portrayal of Trump's boycott announcement. "The press predictably jumped to cover his tweet, creating yet another distraction from any real issues that Mr. Trump might be questioned about," the spokesperson said.

Trump's office replied by saying "Mr. Trump stands by his statement made earlier today" and pointing out the high ratings Stephen Colbert's show received when Trump stopped by on Tuesday night.

What happened between Fox and Trump?

Trump previously threatened to boycott Fox News in the wake of the first Republican primary debate six weeks ago on the grounds that the network's moderators -- particularly Kelly -- had been unfair to him.

The two parties reached detente after Fox News chairman and CEO Roger Ailes called Trump to assure him that he would be treated fairly.

But the truce was exceedingly fragile. Trump still complained from time to time about Fox's coverage.

After the second primary debate of the season, last week, Trump was booked to appear this Thursday night on "The O'Reilly Factor," the highest-rated show on cable news.

O'Reilly even promoted the upcoming Trump interview while appearing on "Jimmy Kimmel Live," which was taped Monday evening.

By Monday night, however, Trump was souring on O'Reilly's show. He fired off a series of angry tweets.

"I am having a really hard time watching Fox News," Trump tweeted. He complained that O'Reilly's show had been "very negative to me" because its guests were all "Trump haters."

He also resumed his critiques of Kelly, who has drawn Trump's fire ever since her grilling of the candidate during the first debate.

"She is the worst -- all anti-Trump!" Trump tweeted Monday night. "Terrible show."

He also singled out Lowry as "truly one of the dumbest of the talking heads."

On Tuesday night, Trump wrote, "Do you ever notice that lightweight Megyn Kelly constantly goes after me but when I hit back it is totally sexist. She is highly overrated!"

In a wink to his fans, some of whom wrongly thought Kelly's post-debate vacation was a suspension, he also wrote, "I think Megyn Kelly should take another eleven day 'unscheduled' vacation."

How long will the Trump blackout last?

For Fox News, the boycott -- whether instigated by Ailes or Trump -- means it will be cut off from the Trump ratings machine. By the same token, Trump will miss out on access to the millions of viewers who tune into Fox News every night for coverage of the 2016 race.

Trump, who gave a relatively subdued performance at the Sept. 16 GOP debate, is down 8 points in the latest CNN/ORC national poll. Meanwhile, rivals like Carly Fiorina and Ben Carson have been on the rise, and commanding more and more media attention.

But a post-debate poll by Fox, published on Wednesday night, showed Trump still leading the GOP pack with 26% support now, holding steady from the 25% support a Fox poll found for him in mid-August.

Carson is up to 18%, from 12% before, according to the Fox poll, and Fiorina is up to 9%, from 5% before.

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