Former Progressive Conservative Prime Minister Brian Mulroney says that Republican Donald Trump’s proposal on trade would push the United States into a “depression very, very quickly.”

“If you talked to anybody who has been in government in a serious way in the last 50 years, they’ll tell you all you’ve got to do is look at the 1930s,” he told Power Play on Monday.

Mulroney, who signed the North American Free Trade Agreement in 1992, said Trump’s proposal to slap large tariffs on imports from countries like China, Mexico and Canada would “shut down the American economy.”

He said NAFTA proved to be a huge success for the U.S., where it has created millions of jobs and led to a five per cent unemployment rate.

Mulroney also said Trump’s plan to block immigration of Muslims would be perilous for the economy.

“Great countries like Canada and the United States are built on immigrants,” he said. “We need more immigration, not less.”

Immigrants bring “dynamism … appreciation, enthusiasm, and they bring the genius of a man with his family looking for freedom and advancement,” he added. “This is what kept Canada in the prosperity business for so long -- and the United States.”

Mulroney also warned that Trump’s comments about the North Atlantic Treaty Organization (NATO) being “obsolete” are dangerous in light of new shared threats from terrorism.

In fact, he said Canada should live up to a previous commitment to double its defence spending from one per cent of GDP to two per cent, and commit more troops to NATO and United Nations peacekeeping, so that the U.S. no longer has to bear an oversized burden. The U.S. spends 3.5 per cent of GDP on defence.

Mulroney conceded the possibility that Trump would be more moderate in office than while campaigning.

“I’ve been friendly with Democratic and Republican presidents, and on foreign policy they all tended to hew to the same line,” he said.

“There was a good deal of moderation in their actual approaches, with some exceptions of course in Iraq.”