Push for Nafta Overhaul May Fall Short, U.S. Negotiator Says In remarks ahead of a third round of talks beginning on Saturday in Ottawa, Robert Lighthizer, the United States trade representative, said negotiators were “moving at warp speed, but we don’t know whether we’re going to get to a conclusion, that’s the problem.” “We’re running very quickly — somewhere,” Mr. Lighthizer said in a rare question-and-answer session at the Center for Strategic and International Studies, a Washington-based think tank. WASHINGTON — The top United States trade negotiator said Monday that it was unclear whether Canada, Mexico and the United States could reach a deal to overhaul the North American Free Trade Agreement within the ambitious timetable set by the Trump administration. “The political calendar is such that if we don’t get a deal more or less by the end of the year... it will get harder and harder,” Commerce Secretary Wilbur Ross, who helps lead the trade agenda, said last week. The Trump administration has carved out a narrow path to victory on Nafta, pledging to hammer out substantial changes in a matter of months to a sweeping pact governing most of the North American economy. The White House is particularly eager to show progress on the trade agenda — one of President Trump’s signature campaign issues — given the failure of Congress to repeal and replace the Affordable Care Act and the uncertainty about tax reform. They fear approval could be complicated by a series of events, including Mexico’s presidential election on July 1, 2018, midterm elections in the United States and provincial elections in Canada.