A coalition of former Republican-nominated U.S. attorneys on Thursday spoke out against President Donald Trump’s unsubstantiated claims of voter fraud in the 2020 presidential election, saying the U.S.’s “very legitimacy as a nation of laws, not men, depends on getting this right.”

The letter, signed by 19 ex-federal prosecutors, comes as Trump falsely and prematurely claims he has won the election, even as votes in several key states continue to be counted. The president has suggested that he would take a case on the election to the U.S. Supreme Court, although legal experts are dubious of what that path would look like.