In an extraordinary open letter, the Pentagon's former defense secretaries and five former chairmen of the Joint Chiefs of Staff have warned that the "extreme strain of political polarization'' in the US and recent events at home and abroad have put civilian-military relations at a low point. Two former Trump administration defense secretaries, Mark Esper and James Mattis, who were removed from office by President Donald Trump, signed the letter, as did former Pentagon secretaries Ash Carter, William Cohen, Robert Gates, Chuck Hagel, Leon Panetta and William Perry.