President-elect Donald Trump on Monday morning threatened to put an end to President Barack Obama’s efforts to normalize relations with Cuba. The threat comes three days after the death of the island nation’s former leader, Fidel Castro. “If Cuba is unwilling to make a better deal for the Cuban people, the Cuban/American people and the U.S. as a whole, I will terminate deal,” Trump tweeted. Republicans vociferously criticized Obama’s moves, starting in 2014, to normalize relations with the communist country. Embassies have since opened in Washington and Havana, as Obama has indicated he wants to end the U.S. trade embargo. Meanwhile, American Airlines and JetBlue on Monday flew commercial routes from New York and Miami to Havana for the first time in decades.