The U.S. Senate looks poised to vote this week on the contentious national debate over GMO labeling, but as the potentially landmark vote looms, facts that should be at the heart of the discussion are being lost.

And in that void, the issue has become highly divisive, pitting many Democrats who want mandatory labeling of foods made with genetically engineered crops against Republicans who favor a measure from Sen. Pat Roberts that would block mandatory labeling, including state laws like one in Vermont set to take effect July 1. A similar measure to block mandatory labeling passed the House of Representatives last July.

Compromise measures are being drafted by both sides, and some close to the talks say Vermont's law and other state labeling measures will likely be sacrificed for such compromise. Food industry players remain resolved against labels that would easily identify a food product as containing GMOs, saying they would needlessly scare consumers away. Meanwhile, clear labeling is precisely what consumer groups demand.

The outcome could be determined by Wednesday, insiders say. But before lawmakers weigh in, it's worth a look at how the United States came to such a sharp divide, how certain facts have fallen by the wayside, and to return for a moment to the core of the call by consumers for labeling.

The grassroots groups that for years have demanded labeling have done so for two simple reasons: They worry that the genetically engineered crops on the market now carry potential and actual risks for human health and the environment. And they lack confidence in the regulatory and corporate entities that say those concerns are unsubstantiated.

Trust us, the corporations and the regulators say. "Food companies are in the best position to determine what type of information meets the needs and desires of their customers," Monsanto Co. the world's largest GMO crop developer, says on its website in a statement opposing mandatory labeling.

But that trust has been hard to come by for many consumers. Both the agencies and the companies involved have less-than-stellar track records when it comes to allowing health and environmental ills into the marketplace, to put it mildly. (PCBs, Asbestos, PFOA acid, etc...)

So consumer groups look for the truth. And one truth is that the current regulatory structure requires no independent safety testing of genetically engineered crops before they are commercialized for food. There is but a voluntary consultation process between the Food and Drug Administration and biotech crop companies, and the FDA acknowledges "it does not conduct a comprehensive scientific review of data generated by the developers." It is also a fact that the U.S. Department of Agriculture and the Environmental Protection Agency (EPA) rely largely on the companies that profit from the GMO products to provide the research the agencies use to evaluate how these GMOs impact other plants and the environment.

Another truth is this: It's been 20 years since the first genetically engineered crop was commercialized and despite continued promises that GMO crops would bring a range of nutritional benefits to consumers, fight killer crop diseases, create crops that flourish even during drought, and help the environment, the reality has been something starkly different.

Most of the GMO corn and soybeans, and other crops that spread across well over 100 million acres of U.S. farmland are genetically engineered not with added vitamins or to survive harsh weather or disease, but to withstand direct dousing of the weedkilling chemical called glyphosate, which the World Health Organization classifies as a probable human carcinogen. These glyphosate-tolerant crops are supposed to make it easier for farmers to knock out yield-choking weeds. But as farmers have planted more of these herbicide-tolerant crops, weeds have developed resistance, so farmers have been spraying larger volumes of the herbicide on their fields. This herbicide linked to cancer is now the most widely used herbicide in the world.

Globally, glyphosate use has risen almost 15-fold since GMO glyphosate-tolerant crops were introduced in 1996. Glyphosate is now found in air and water samples and human urine samples. The trend has been documented by U.S. government researchers as well as state and private scientists. It's not a matter of dispute. But it is something that those fighting to block mandatory labeling ignore.

These glyphosate residues have also been found within certain foods in limited testing. The USDA and FDA annually test thousands of food for other pesticide residues to make sure such residues don't hit unsafe levels. But neither agency tests for glyphosate residues, leaving consumers to simply hope that those residue levels are not high enough to be harmful. The FDA only last month said it will start doing some limited testing for glyphosate residues in food later this year.

Those opposing mandatory labeling argue that consumers have nothing to fear. They discount scientists who say the jury is out on safety and more research is needed. They repeat the claims of Monsanto and other crop developers, including the widely repeated assertion that GMOs mean more abundant food, even though USDA research shows yield data comparing GMO crops to conventional crops is mixed.

A March 10 USA Today editorial that called mandatory GMO labeling a "bad idea" is a prime example of how these inconvenient truths are often ignored. The editorial made not a single mention of glyphosate use with GMOs, and said mandatory labeling "plays to unfounded fear."

The fact is that GMO crops were developed by Monsanto for the purpose of selling more glyphosate. Other companies also sell glyphosate-based herbicides now that Monsanto's patent has expired but Monsanto remains a top seller of the herbicide. The newest GMO crops coming to market are those that will also tolerate dicamba and 2,4-D herbicides along with glyphosate.

"That is why I got into the fight," said Gary Hirshberg, chairman of the Just Label It campaign and head of Stonyfield Farm, an organic yogurt producer based in New Hampshire. "GMOs equal herbicide proliferation."

To the GMO crop developers' credit, genetically engineered insect-resistant crops did at one time help farmers reduce insecticide use, though insect resistance has been eroding that benefit and insecticide sales have grown in recent years. It is also true that a range of other GMO crops are on the drawing board or in limited commercial circulation. Last year a new type of apple that doesn't turn brown was approved by the FDA. Researchers are hoping to develop a GMO citrus tree that wards off diseases that can hurt orange production. Researchers are also working on food with enhanced protein or vitamin content.

But today the truth is this: The bulk of the GMOs used in our food are not about improving nutrition or the environment, or creating more affordable and abundant food. They have been, and still are, about selling more agrichemicals. Monsanto gets close to one-third of its $15 billion in annual revenues from glyphosate-related sales. The total market is pegged at reaching $8.8 billion by 2019 due to the spread of GMO crops.

For consumers who worry about conflicting science on safety, and adding more pesticides into an already fragile environment, their fears are not unfounded. They want to be able to vote with their pocketbooks for or against products they believe might be unsafe for themselves and/or the environment.

Lawmakers should look at the history and the facts of GMO crops and should cast their votes in the interests of those who buy and consume GMO foods, not those who profit from them.