On 8 August 2016, a letter appeared purporting to be from a group of former national security officials, all Republicans, and all vowing not to vote for Donald Trump and declaring him a threat to the nation:

The undersigned individuals have all served in senior national security and/or foreign policy positions in Republican Administrations, from Richard Nixon to George W. Bush. We have worked directly on national security issues with these Republican Presidents and/or their principal advisers during wartime and other periods of crisis, through successes and failures. We know the personal qualities required of a President of the United States.

None of us will vote for Donald Trump.

From a foreign policy perspective, Donald Trump is not qualified to be President and Commander-in-Chief. Indeed, we are convinced that he would be a dangerous President and would put at risk our country’s national security and well-being.

Most fundamentally, Mr. Trump lacks the character, values, and experience to be President. He weakens U.S. moral authority as the leader of the free world. He appears to lack basic knowledge about and belief in the U.S. Constitution, U.S. laws, and U.S. institutions, including religious tolerance, freedom of the press, and an independent judiciary.

In addition, Mr. Trump has demonstrated repeatedly that he has little understanding of America’s vital national interests, its complex diplomatic challenges, its indispensable alliances, and the democratic values on which U.S. foreign policy must be based. At the same time, he persistently compliments our adversaries and threatens our allies and friends. Unlike previous Presidents who had limited experience in foreign affairs, Mr. Trump has shown no interest in educating himself. He continues to display an alarming ignorance of basic facts of contemporary international politics. Despite his lack of knowledge, Mr. Trump claims that he understands foreign affairs and “knows more about ISIS than the generals do.”

Mr. Trump lacks the temperament to be President. In our experience, a President must be willing to listen to his advisers and department heads; must encourage consideration of conflicting views; and must acknowledge errors and learn from them. A President must be disciplined, control emotions, and act only after reflection and careful deliberation. A President must maintain cordial relationships with leaders of countries of different backgrounds and must have their respect and trust.

In our judgment, Mr. Trump has none of these critical qualities. He is unable or unwilling to separate truth from falsehood. He does not encourage conflicting views. He lacks self-control and acts impetuously. He cannot tolerate personal criticism. He has alarmed our closest allies with his erratic behavior. All of these are dangerous qualities in an individual who aspires to be President and Commander-in-Chief, with command of the U.S. nuclear arsenal.

We understand that many Americans are profoundly frustrated with the federal government and its inability to solve pressing domestic and international problems. We also know that many have doubts about Hillary Clinton, as do many of us. But Donald Trump is not the answer to America’s daunting challenges and to this crucial election. We are convinced that in the Oval Office, he would be the most reckless President in American history.