HAMILTON, Canada

Canada's outgoing Prime Minister Justin Trudeau extended greetings Monday to US President Donald Trump on his return to the White House for a second term.

"On behalf of the Government of Canada, I extend my congratulations to Donald J. Trump on his inauguration as President of the United States of America for a second term," Trudeau said in a statement, describing relations between the two countries as "the world's most successful economic partnership."

Saying that Canada and the US are "each other's largest trade partners, with a relationship that creates millions of jobs," Trudeau said the partnership "attracts billions in investment into the continent" while keeping their citizens safe.

He expressed Canada's commitment to strengthening the "beneficial relationship," and said: "We are making massive investments to bolster cross-border trade, reinforce our supply chains, and create jobs on both sides of the border."

Trudeau highlighted the importance of cooperation for continued success and said, "We are strongest when we work together, and I look forward to working with President Trump, his administration, members of the United States Congress, and officials at the state and local levels to deliver prosperity for our peoples – while protecting and defending the interests of Canadians."

Since his election victory in November, Trump has referred to Canada as the "51st state."

Trump has threatened to slap a 25% tariff on Canadian imports unless Canada takes steps to significantly reduce the flow of drugs and illegal immigrants crossing into the US. He similarly threatened Mexico with the tariffs.