Leave military out of it, former defence secretaries tell Trump

All 10 former US defence secretaries still living, including two who worked for Donald Trump, have called for the president and his supporters to accept he lost the election and warned against attempts to involve the military in his increasingly desperate efforts to overturn the result.

In an unprecedented joint letter published in the Washington Post, the defence secretaries addressed the worst fears of what could happen in 17 days of Trump’s administration remaining before Joe Biden’s inauguration: an attempt by Trump to foment a crises with the aim of triggering a military intervention in his last-ditch struggle to hold on power.

“Efforts to involve the US armed forces in resolving election disputes would take us into dangerous, unlawful and unconstitutional territory,” the letter said.

Related: 'I just want 11,780 votes': Trump pressed Georgia to overturn Biden victory

“Civilian and military officials who direct or carry out such measures would be accountable, including potentially facing criminal penalties, for the grave consequences of their actions on our republic.”

Among the signatories were James Mattis and Mark Esper, who both served as defence secretaries in the Trump administration. Esper openly contradicted Trump in June by insisting there were no grounds for invoking the Insurrection Act, which allows for the deployment of US troops on American streets in extreme circumstances.

Dick Cheney, defence secretary under George HW Bush, and vice-president to his son, George W Bush, and Donald Rumsfeld, defence secretary in the younger Bush’s administration, also signed. The other signatories were William Perry and William Cohen, defence secretaries in the Bill Clinton administration; Leon Panetta, Chuck Hagel and Ashton Carter, who served under Barack Obama; and Robert Gates, who served under both the younger Bush and Obama.

“Transitions, which all of us have experienced, are a crucial part of the successful transfer of power. They often occur at times of international uncertainty about US national security policy and posture,” the former defence secretaries wrote. “They can be a moment when the nation is vulnerable to actions by adversaries seeking to take advantage of the situation.”

They called on the current defence secretary, Christopher Miller, and his officials to resume cooperation with the Biden transition team, who had complained their briefings had been cut off and the Pentagon had ceased answering their inquiries.

The Washington Post quoted Eric Edelman, a former US ambassador and defence official, as saying the genesis of the remarkable letter was a conversation he had with Cheney about how the military might be used in coming days.

There are concerns over unrest on Wednesday when a dozen Republican senators say they will challenge the normally routine congressional ratification of the electoral college result.

Trump has urged his supporters to rally in Washington, tweeting: “Be there, will be wild!” The far right Proud Boys are expected to be among the pro-Trump crowd in the capital.

Cohen told the Post he was concerned by the mention of the possibility of martial law by the former Trump national security adviser Michael Flynn, especially after Trump’s use of the military and other federal forces to remove protesters outside the White House in June.

“It’s a very dangerous course of action that needs to be called out before it happens,” Cohen said.

“[It is] so important to see the country’s secretaries of defence sending this message,” wrote Risa Brooks, a Marquette University associate professor studying civil-military relations and political violence. “The civilians who run the military need to be front and centre in conveying this message to the public and not leave it to the military alone.”