In a last-ditch effort to stop Donald Trump’s likely nomination as the Republican Party’s candidate for president, a group of more than 50 conservative foreign policy experts have banded together in an open letter condemning the real estate magnate as unfit for the office.

From stating that he’ll make Japan — a close U.S. ally — pay for its longstanding American support, to declaring generational warfare on terrorists, Trump’s rhetoric appears to have finally crossed a line for those conservatives that have made their careers in foreign policy.

The letter’s signatories include Frances Townsend, a former homeland security adviser to President George W. Bush, and Dov Zakheim, a former undersecretary of defense in the same administration. The letter was published Wednesday night on the foreign policy site War on the Rocks.

The letter was the byproduct of a Twitter back and forth by Eliot Cohen, a former State Department official also under Bush and Bryan McGrath a one-time naval adviser to former Massachusetts governor Mitt Romney’s 2012 campaign.

“Do you want to do something about this?” McGrath recalls writing to Cohen, and soon they were bouncing a draft of the letter to their respective address books.

The short, bullet-pointed document hits Trump on issues ranging from his praise of Russian President Vladimir Putin, his nonchalance about torture, being “fundamentally dishonest” and his anti-Muslim rhetoric.

On Friday, Reuters reported that Trump is being “informally advised” by retired U.S. Army Lt. Gen. Michael Flynn. Flynn was chief of the Defense Intelligence Agency under President Obama from 2012-2014, and has long advocated for a warmer relationship with Russia.

“[Trump’s] vision of American influence and power in the world is wildly inconsistent and unmoored in principle. He swings from isolationism to military adventurism within the space of one sentence,” the letter reads.

The letter comes just days after Michael Hayden, the former head of the Central Intelligence Agency and the National Security Agency, said that the U.S. military might disobey orders if Trump becomes President.

McGrath said that he has faced some criticism regarding the letter, including that its signers are the exact type of establishment Republicans that Trump has been railing against. He also said that some have interpreted the letter as leaving open the possibility that instead of voting for Trump, McGrath and his co-signatories might instead support former secretary of state Hillary Clinton.

“I would never write a letter or sign a letter that carries that kind of implication,” McGrath said. “The only implication here is that we’re not going to support Donald Trump.”

McGrath added that he hopes voters see that the letter constitutes the views of “a reasonable group of people who work in this field” and that they realize Trump is unsuited for the job of president.

“I want to be on record saying that this man is not presidential material,” McGrath said. “And this was the best way I could do it and bring some friends along.”

(c) 2016, The Washington Post · Thomas Gibbons-Neff