Thomson Reuters
Donald Trump.
The experts stated that while they disagree on many issues, they all agree that the Republican presidential frontrunner's administration would not be good for the country.
"We the undersigned, members of the Republican national-security community, represent a broad spectrum of opinion on America's role in the world and what is necessary to keep us safe and prosperous," they wrote in the letter, which was published by the foreign-policy website War On The Rocks.
The national-security leaders added: "We have disagreed with one another on many issues, including the Iraq war and intervention in Syria. But we are united in our opposition to a Donald Trump presidency."
The letter includes some notable names in foreign policy - Frances Townsend is a former homeland security adviser, Michael Chertoff is a former secretary of homeland security, Max Boot is a senior fellow at the Council on Foreign Relations and well-known foreign policy commentator, and Robert Kagan is a leading neoconservative and historian.
The letter runs down a list of objections to Trump's statements and foreign-policy positions. Their reasons are many, but a few of the most strongly worded are below:
His 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.
His hateful, anti-Muslim rhetoric undercuts the seriousness of combatting Islamic radicalism by alienating partners in the Islamic world making significant contributions to the effort. Furthermore, it endangers the safety and Constitutionally guaranteed freedoms of American Muslims.
His admiration for foreign dictators such as Vladimir Putin is unacceptable for the leader of the world's greatest democracy.
He is fundamentally dishonest. Evidence of this includes his attempts to deny positions he has unquestionably taken in the past, including on the 2003 Iraq war and the 2011 Libyan conflict. We accept that views evolve over time, but this is simply misrepresentation.
The letter's conclusion called Trump "utterly unfitted to the office" of president.
"Mr. Trump's own statements lead us to conclude that as president, he would use the authority of his office to act in ways that make America less safe, and which would diminish our standing in the world," the letter stated.
"Furthermore, his expansive view of how presidential power should be wielded against his detractors poses a distinct threat to civil liberty in the United States. Therefore, as committed and loyal Republicans, we are unable to support a Party ticket with Mr. Trump at its head."
While some foreign-policy experts have criticized Trump's proposed national-security policies, others have defended him. Doug Bandow, a senior fellow at the Cato Institute who specializes in foreign policy, wrote an opinion column for Forbes saying that, Trump is the best GOP candidate on foreign policy.
"Trump obviously is not a deep thinker on foreign policy or anything else," Bandow wrote. "Nevertheless, on these issues he exhibits a degree of common sense lacked by virtually every other Republican candidate. The GOP needs to have serious debate over foreign policy."