The U.S. leader, who is now in Singapore to meet with his North Korean counterpart, said "Fair Trade is now to be called Fool Trade if it is not Reciprocal," and called into question the trading relationship between his country and some of its closest allies.
Trump followed up that message with another tweet:
The president also claimed that the U.S. is responsible for most of the cost of the inter-governmental military alliance, the North Atlantic Treaty Organization, to protect "the many of these same countries that rip us off on Trade."
About an hour after the series of Twitter posts, Trump reiterated his message in another tweet:
Trump has been lashing out at Canadian Prime Minister Justin Trudeau since Saturday after he refused to endorse the G-7 declaration calling for a reduction in various barriers to trade, including tariffs.
He slammed Trudeau in a Twitter post for being "very dishonest & weak" after Trudeau held a news conference that called the U.S. tariffs "kind of insulting."
White House economic advisor Larry Kudlow also accused Canada of making "polarizing" statements about the United States' trade policy, and said Trump had to pull out of a joint statement because his Canadian counterpart had "stabbed us in the back."
Trump has been accusing his country's closest allies, including Canada, of treating the U.S. unfairly — a point that many experts said is not true.
Trump had specifically singled out Canada's 270 percent tariff on dairy products for limiting American products' access to its northern neighbor. While Canada indeed imposes that sized tariff, the U.S. has an overall goods and services trade surplus with Canada at $8.4 billion in 2017, according to Office of the United States Trade Representative.
The U.S., however, did register a trade deficit of $17.5 billion with Canada last year when only goods are counted and services are not, the USTR said. That's likely the "17B" Trump was referencing in his Monday morning tweet. According to Canadian data, meanwhile, the country's trade surplus with the U.S. when counting only goods amounted to around $126.74 billion Canadian dollars — which comes out to about $97.75 billion. That could potentially be the "almost 100 Billion Dollars" that the president cited.
The White House did not immediately respond to CNBC's request for clarification on the figures Trump tweeted. Many economists stress that trade is best understood as a combination of both goods and services, so only taking half of the equation may not fully reflect reality.
Paul Krugman, a Nobel-winning economist and New York Times op-ed contributor, said on Twitter that Trump's "policy agenda is almost entirely directed at problem we don't have."