President Donald Trump’s repeated threats to pull the U.S. out of the North American Free Trade Agreement have kept the U.S. ag sector on edge for months, but many have been able to dismiss the comments as just part of a particularly aggressive negotiating tactic.That time has passed, though, and farm sector leaders are expressing concern that Trump may have no intention of allowing the current NAFTA negotiations to succeed.Whether it’s through so-called “poison pill” proposals designed to doom the talks to failure or whether the White House will simply pull the plug, severing decades-old ties with Mexico and Canada, the prospect of an end to NAFTA is prompting an onslaught of lobbying from CEOs, lawmakers and state leaders across the country.The dairy industry has a lot to lose if NAFTA is scuttled. Mexico - with its 135 million consumers - is the largest foreign market for U.S. dairy products, and the trade pact insures that there are no tariffs on U.S. shipments south of the border.