Donald TrumpDonald TrumpSanders: FBI's investigation of wife won’t be a ‘distraction’ Schiff: Obama's delayed response to Russian interference 'a very serious mistake' The Memo: GOP pushes Trump to curb Mueller attacks MORE is ratcheting up his already ferocious assault against his chief rival in the race for the Republican presidential nomination, Ben Carson.

Following an explosive 95-minute-long rant Thursday night in Iowa that some in the media described as “off the rails," Trump is refusing to relent, releasing a short but sharp Instagram video underlining his challenge to the veracity of Carson’s now-infamous stabbing story.

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The Friday the 13th-themed ad opens with Carson recounting his attempt to stab a friend as a teen as eerie music reminiscent of the classic horror film "Halloween" plays in the background.

A neighbor of Carson’s, in a CNN interview, is then shown rejecting the notion that the retired neurosurgeon would try to stab another person.

“Violent criminal? Or pathological liar?” the ad asks. "We don’t need either as president.”

According to Carson's business partner Armstrong Williams, when asked for his response to Trump's latest line of attack, Carson simply answered “pray for him."