Even the notoriously brash billionaire backs down from fight with GMO seed giant.

Clear Lake, Iowa — What comes up, must go down. As the race for the presidential campaign field of 2016 heats up, Donald Trump's poll numbers have started to slip. The first place this has been noticed is in Iowa, where the latest Des Moines Register Poll has Trump trailing Ben Carson by 9 points.

In a quick retort to his dipping poll numbers, Donald Trump (or someone in control of his Twitter feed) retweeted a humorous tweet from one of his followers that accidentally took a swipe at the intelligence of the Iowa voter and a jab at the Midwestern state's number one commodity export — Monsanto's genetically engineered corn. According to USDA statistics, 94 percent of corn grown in Iowa is genetically engineered and 97 percent of the soybeans in the state are GMO as well.

"Donald Trump just learned the first lesson of Presidential politics, said Dave Murphy, founder and executive director of Food Democracy Now! "He can talk trash about his fellow Republican candidates or attack Democrats, but he can't insult Iowa voters. Or link their intelligence to Monsanto's GMO corn."

Trump quickly backed down, erasing the tweet from his feed, but a screenshot captures what was sure to be a barnburner Tweet before it could really go viral.

The GMO labeling movement is happy to have Donald Trump's support, it's refreshing to hear a Republican presidential candidate stand up to Monsanto and the industrial farm lobby, even if it is only for a few minutes on Twitter.

"The fact that even billionaire Donald Trump would back down from Monsanto, should give Americans pause," Murphy added. "While the real and potential harm these products cause the environment and human health is no joking matter, it's an important reminder that all Americans have the right to know if their food has been genetically engineered in a laboratory, which is something that everyone can agree on, from billionaires to Iowa corn farmers."

Right now the battle to label GMOs is heating up in Washington DC and politicians should ​be on notice.

This week the Senate Agriculture Committee held a hearing on crop biotechnology, the first one in ten years, where every member of the committee took time to remind their audience that GMOs are safe, despite a growing pile of evidence pointing to potential harm.

On March 23, 2015, the World Health Organization's research arm the International Agency for Research on Cancer declared that glyphosate, the main chemical ingredient in Monsanto's best-selling weedkiller Roundup was linked to cancer in humans and lab animals.

Clearly, the message of Monsanto's legacy of producing toxic products has gotten to Donald Trump.

The real question is, what does billionaire Donald Trump know about Monsanto's products that the U.S. Senate is afraid to admit?