Former prime minister Paul Martin is urging Canada and other world leaders to fight back against Donald Trump’s “America First” leadership style, warning that the U.S. president’s policies are increasingly threatening global multilateralism.

Martin, who served as Canada’s prime minister from 2003 to 2006, said that strong leadership is needed as deteriorating cooperation has hurt the world economy.

“I think it has to be a very public fight,” Martin told BNN Bloomberg’s Amanda Lang.

“The numbers demonstrate unequivocally that the loss of momentum in the global economy – which has got everyone worried at the present time – is the direct result of the world failing to work together. And that’s really been the outcome of the American position.”

Martin’s comments come amid multiple reports that China-U.S. trade talks are stalling, as the dispute over Huawei Technologies Co. drags on and with Trump complaining that China isn’t buying the volumes of U.S. agricultural goods that President Xi Jinping had promised.

When it comes to Canada, Martin says the country needs to show the same kind of leadership as when the Group of 20 was created after the 2008 financial crisis struck.

“We can say, ‘Listen, the fact is, we have to cooperate and we have to share sovereignty if we want to protect sovereignty,” Martin said. “In other words, globalization is not a government choice – globalization is a reality.”

On Canada’s tense relationship with China, Martin says the country did “the right thing” in abiding by the United States’ extradition request of Huawei Chief Financial Officer Meng Wanzhou, but added that he understands difficulties the Canadian government is facing as a result.

“You’ve got to stand up to the bully. And you’ve got to stand up to bullies no matter where they are,” Martin said. 

“We’ve got to be prepared to stand up to those who would [rather] not have the world work … We’ve got to make it very clear: You may think you’re getting your way, but in fact the world’s going to get in your way because nobody can stand alone here.”