Fox News anchor Megyn Kelly returned Monday night to host "The Kelly File" following a 10-day vacation, but her extended R&R seemed to have no relaxing effect on her loudest critic: Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE.

In a series of late-night tweets, Trump accused Kelly of being “off her game,” and suggested she “must have had a terrible vacation” because she was “afraid to confront” her guest, Cornel West, on the subject of immigration.

Trump followed up his tweets with a couple of retweets from supporters who called Kelly a “bimbo” and her show “a waste of an hour on Fox.”

"@mstanish53: @realDonaldTrump @megynkelly The bimbo back in town . I hope not for long ." — Donald J. Trump (@realDonaldTrump) August 25, 2015

“The bimbo back [sic] in town,” said one tweet, which Trump reposted into his own timeline. “I hope not for long."

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The Republican front-runner’s feud with Kelly — sparked in the aftermath of the first GOP debate, which Kelly co-moderated — reached a crescendo shortly before her temporary leave of absence, when Trump made a comment appearing to reference menstruation as a reason for a line of questioning he believed was unfair.

He went on to suggest several times that Kelly’s vacation was ordered by higher-ups at the news station as a result of the fallout from their post-debate friction.

Fox News pushed back on those claims, saying the time off was scheduled months in advance.

Unfazed, Trump repeated his allegation tonight on Twitter.

"I liked The Kelly File much better without @megynkelly,” the billionaire businessman tweeted. "Perhaps she could take another eleven day unscheduled vacation!"

I liked The Kelly File much better without @megynkelly. Perhaps she could take another eleven day unscheduled vacation! — Donald J. Trump (@realDonaldTrump) August 25, 2015

UPDATE: Fox News chief Roger Ailes and a host of personalities from the cable network fired back at Trump on Tuesday. Ailes said Trump's latest attack was "unacceptable."