Robert Lighthizer was the public face of arduous, year-long talks to rework NAFTA, but as he savoured a successful conclusion in the White House Rose Garden on Monday, the US trade representative singled out another man as the deal's architect.

"I've said before, and I'll say again, this agreement would not have happened if it wasn't for Jared," Lighthizer told reporters.

The 70-year-old veteran negotiator was referring to Jared Kushner, more than 30 years his junior and Donald Trump's son-in-law, whom the president had asked to help out on trade early in the presidency, especially on Canada and Mexico.

While Kushner's time in the White House has been turbulent - Chief of Staff John Kelly temporarily stripped him of his security clearance earlier this year and he has been criticized for his dealings with the Middle East - his role in keeping the North American Trade Agreement afloat was fundamental, multiple sources said.

A 37-year-old real estate tycoon married to Trump's daughter Ivanka, Kushner has the trust of his father-in-law, and crucially, is close to Lighthizer, a Canadian source with knowledge of the talks said.

His friendship with Mexican Foreign Minister Luis Videgaray, whom he knows from Wall Street, helped diffuse several blowups in that relationship and get a U.S.-Mexican deal over the finish line in August, another source close to the talks said.

"The deal fell apart more than once. And in every occasion it was one person that always found a way to put it back together: Jared Kushner," Videgaray told Reuters.

Similarly, from early on in the negotiations, two of Canadian Prime Minister Justin Trudeau's most trusted advisers - chief of staff Katie Telford and private secretary Gerald Butts - forged ties with Kushner, Hassan Yussuff, president of the Canadian Labour Congress, said in a phone interview. Yussuff was part of the NAFTA advisory council for Chrystia Freeland, Canada's lead negotiator in the talks and the country's foreign minister.

A second Canadian source said Telford and Butts flew to Washington to meet Kushner in the early days of the presidency.

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