President Trump on Saturday threatened to exclude Canada from a new NAFTA deal and “terminate” the trade pact entirely if Congress gets involved in negotiations. “There is no political necessity to keep Canada in the new NAFTA deal. If we don’t make a fair deal for the U.S. after decades of abuse, Canada will be out,” Trump wrote on Twitter. He went on to warn Congress, which has authority over trade agreements, “not to interfere” or he will scrap NAFTA altogether. Under NAFTA rules, Trump can withdraw the U.S. from the pact if he gives six months’ notice, but legal experts say Congress can and likely would put up legal obstacles to block the move. Trump’s comments came after the White House extended NAFTA negotiations with Canada that were due to end Friday after striking a revised trade deal with Mexico earlier this week. Robert E. Lighthizer, the United States trade representative, said in a statement Friday that it would be up to Canada to decide whether or not to remain in NAFTA and sign a new trade agreement. Negotiations with Canada are due to resume on Wednesday.