A group of 50 former national security officials, all of whom have served Republican presidents from Richard M. Nixon to George W. Bush, have signed an open letter calling Donald Trump unqualified to be president and warning that, if elected, “he would be the most reckless President in American history.”

The letter offers a withering critique of the GOP nominee, saying he “lacks the character, values and experience” to be president. The signatories declare their conviction that he would be dangerous “and would put at risk our country’s national security and well-being.”

They state flatly that none of them intend to vote for Trump in November. Some have decided to vote for Hillary Clinton, while others intend to sit out the election or write in another name, said John Bellinger III, a former legal adviser to Condoleezza Rice and the writer of the letter’s first draft.

“We also know that many have doubts about Hillary Clinton, as do many of us,” the letter says. “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.”

Republican leaders and former security officials discussed Republican presidential nominee Donald Trump’s national security qualifications on political shows on Aug. 7. (Bastien Inzaurralde/The Washington Post)

In a statement, Trump said the letter writers share the blame for “making the world such a dangerous place.”

“They are nothing more than the failed Washington elite looking to hold onto their power, and it’s time they are held accountable for their actions,” he said.

Trump said the former officials — along with Clinton — took part in the decisions that led to the invasion of Iraq, the deaths of Americans in Benghazi, Libya, and the rise of the Islamic State.

“Yet despite these failures, they think they are entitled to use their favor trading to land taxpayer-funded government contracts and speaking fees,” he said.

Although no former secretaries of state signed the letter, it carries the signatures of Michael Chertoff and Tom Ridge, former secretaries of homeland security; Michael Hayden, a former director of the CIA and the National Security Agency; John Negroponte, a former director of national intelligence and deputy secretary of state; Robert Zoellick, who also was a deputy secretary of state and president of the World Bank and the U.S. trade representative under George W. Bush; Carla Hills, the U.S. trade representative under George H.W. Bush; and William H. Taft IV, a former deputy secretary of defense and ambassador to NATO under the elder Bush.

Also signing the letter were several aides who were senior advisers in the White House, State Department and Pentagon. Among them were Eric Edelman, a national security adviser to then-Vice President Richard B. Cheney, and Bellinger, who worked closely with Rice when she was secretary of state and when she was on the NSC.

Bellinger said that some involved with the letter wanted to wait until September to release their views but that the candidate’s behavior in recent weeks — from his comments on NATO to inviting Russian intelligence to hack Clinton’s emails — galvanized them to move sooner.

The list of Republicans who reject their presidential nominee, Donald Trump, and support his Democratic opponent keeps growing. (The Washington Post)

“This is not about NATO, it’s not about trade, it’s not about Russia, it’s not about cyber. We really wanted to focus on the character, temperament and judgment that we have seen are required of good presidents,” Bellinger said.

Although the signatories all served Republican presidents, many of the criticisms echo those being leveled by the Clinton campaign.

“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,” the letter says of Trump.

Later on, it adds, “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.”

The letter said Trump “lacks the temperament to be President,” and gave a scathing assessment of his ability to take advice, discipline himself, control his emotions and reflect before acting.

“He is unable or unwilling to separate truth from falsehood,” the letter states in a particularly pointed criticism of Trump’s personal traits. “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.”

Bellinger said the letter is not intended to be political.

“What we really wanted to do was to raise the alarm and awareness among voters who may find Mr. Trump attractive in a lot of ways, but do not understand what is required to be president of the United States,” he said. “We are trying to say to them, we have served inside the White House, we have worked with presidents for decades, we know what’s required to be president, and we are deeply concerned Donald Trump does not have these qualifications, the judgment or the temperament.”