Tony DiMare, a third-generation Florida tomato grower, has spent two decades contending with cheap Mexican imports, watching his neighbors abandon crops in their fields and sell off their farms when they couldn't match the price of incoming produce. But emboldened by the Trump administration's hostility toward foreign trade, DiMare and a group of Southeast growers are pushing for tough new protectionist measures against their Mexican rivals - so tough, in fact, that their demands threaten to wreck the negotiations."I'm all about free trade, but it has to be fair," DiMare said."It's Americans first now, right?" he added.As the United States, Canada and Mexico prepare to wrap up a fourth round of talks Tuesday about revisions to the North American Free Trade Agreement, there is growing fear that the talks could collapse around one of several "poison pill" provisions.Those include the Florida tomato growers' demands, which are supported by some berry, melon and pepper producers, for stronger anti-dumping measures - an idea that has been soundly rejected by the Mexicans.The Florida growers' high-stakes campaign for special anti-dumping measures for seasonal produce has also exposed sharp divisions with the rest of America's farmers, who are generally strongly pro-NAFTA and whose livelihoods are on the line if the negotiations falter. "There's a lot of political power resting with a small group of individuals who have a lot to gain," said Joseph Glauber, a senior research fellow at the International Food Policy Research Institute and the former chief economist at the Agriculture Department. "Unfortunately, the special provision you carve out for one interest groups can really backfire for others."