Donald Trump said that a "young intern" is responsible for a tweet his campaign put out Thursday insulting Iowans. Reuters

Donald Trump is not one to hold back on Twitter -- and that was the case Thursday when an insult to Iowans was retweeted by his official account following the release of a poll showing the business mogul candidate behind Ben Carson in the state. The tweet in question: "@mygreenhippo #BenCarson is now leading in the #polls in #Iowa. Too much #Monsanto in the #corn creates issues in the brain?#Trump #GOP." [Monsanto is the giant agricultural biotech company at the center of the genetically modified-foods debate.]

But the candidate says he's not the one who should be held responsible. "The young intern who accidentally did a retweet apologizes," Trump tweeted after the incident.

The tweet has since disappeared from his timeline. Earlier in the day, a Quinnipiac University poll of Iowa Republicans released Thursday showed Ben Carson ahead of Trump in Iowa with an 8 percentage-point lead over the real estate mogul.

Trump has come under fire for tweets before. In July, a campaign photo was uploaded to his Twitter account with an image of Nazis fighting in World War II in the background. "We need real leadership. We need results. Let's put the U.S. back into business!" read the caption.

The tweet was quickly deleted and the Trump campaign responded that its candidate wasn't involved with the tweet. "Mr. Trump has been in Charlottesville, Virginia, all day at the opening of a development. A young intern created and posted the image and did not see the very faded figures within the flag of the stock photo," the statement read. "The intern apologized and immediately deleted the tweet."