[Above: Three former Republican presidents, Ford, Reagan, and George HW Bush, in ads in support of statehood for Puerto Rico, 1993. Details here.]
Republicans flipping out over Puerto Rico becoming a state have forgotten (of course) their party platforms and past presidents:
President Gerald Ford proposed statehood in 1976: "I believe that the appropriate status for Puerto Rico is statehood. I propose, therefore, that the people of Puerto Rico and the Congress of the United States begin now to take those steps which will result in statehood for Puerto Rico. I will recommend to the 95th Congress the enactment of legislation providing for the admission of Puerto Rico as a State of the Union."
President Ronald Reagan favored statehood: "I favor statehood for Puerto Rico and if the people of Puerto Rico vote for statehood in their coming referendum I would, as President, initiate the enabling legislation to make this a reality."
President George H. W. Bush raised the issue of statehood before Congress in his first State of the Union message in 1989: "There's another issue that I’ve decided to mention here tonight. I’ve long believed that the people of Puerto Rico should have the right to determine their own political future. Personally, I strongly favor statehood. But I urge the Congress to take the necessary steps to allow the people to decide in a referendum."
The Republican Party platforms of 2008, 2012 and 2016 also endorsed statehood for Puerto Rico. Of course, 2016 was the last platform the Republican Party has had, since this year all they had to say was "go Trump."