President Donald Trump has repeatedly said Canada should be the 51st U.S. state, erasing the 5,525-mile border the nations share and alleviating the need for tariffs he’s threatened against one of America’s top allies.

President Trump said Thursday that Canada is a “serious contender” to become the 51st state, alleging that America’s neighbor to the north needs US “protection.” Trump, 78, has repeatedly floated the idea of Canada joining the Union — even mockingly referring to outgoing Prime Minister Justin Trudeau as “governor” — and revisited the topic while signing a memorandum ordering reciprocal tariffs on countries around the world.