Canada’s ambassador to the United States, David MacNaughton, is leaving his post at the end of the month after protracted and at times heated renegotiations of the North American Free Trade Agreement appear to have taken their toll.

“I’ve never done anything in my life that has been as difficult as this, physically, emotionally, and part of that is just realizing what the stakes are,” he told reporters during a Thursday news conference at our embassy in Washington D.C., where he announced his resignation.

MacNaughton, who was Canada’s point man for the 13-month negotiations, thanked Foreign Affairs Minister Chrystia Freeland and Prime Minister Justin Trudeau for their support, as well as that he received from politicians across the aisle.

“The rallying around of all Canadians when we faced what was really an existential threat, The President of the United States had campaigned against NAFTA, and said he was going to rip the agreement up,” MacNaughton recalled.

“Our dependence on the U.S. Market for our prosperity was certainly being challenged. And because we were able to achieve what I think is a remarkable result, I leave here with some pride in what we have accomplished.”

The longtime Liberal Party strategist, cabinet advisor and former chairmen of public relations firm StrategyCorp was tapped by Trudeau in March of 2016 to succeed former New Democrat premier Gary Doer, who held the post since 2009.

MacNaughton began his role as Canada’s top diplomat to the United States at the twilight of Barack Obama’s two-term presidency, when relations between the two countries and its leaders were sound.

This changed dramatically, however, following the election of Donald Trump, whose ‘America First’ campaign was predicated largely on restructuring outdated trade deals like NAFTA, or scrapping them altogether.

During the negotiations, President Trump’s application of tariffs against steel and aluminum entering the U.S. from Canada over “national security” concerns was dismissed by Trudeau as baseless, yet provided leverage for American negotiators looking for inroads into our dairy and poultry sectors, which they secured.

While the new United States-Mexico-Canada Agreement was ratified by Mexico’s senate in June, the deal still requires ratification by the U.S. and Canadian legislatures.

As the Democrat-controlled U.S. Congress continues to waffle on whether to support the deal, MacNaughton expressed cautious optimism.

“Predicting outcomes in this city is not a science … I am confident that Democrats and Republicans want to get to ‘yes’ on USMCA,” he said.

“I won’t say that it’s a slam dunk by any stretch of the imagination, but I do think that there is broad support even among Democrats.”

Deputy ambassador Kirsten Hillman, who has served alongside MacNaughton since 2017, will take over as acting-ambassador in September.