The letter, posted on foreign policy site War on the Rocks, said that Trump would make the United States “less safe” if elected president. The experts listed their gripes with the frontrunner’s foreign policy platform, including his aggressive advocacy for waging trade wars—”a recipe for economic disaster”—and his inconsistent vision for the United States’ role in global affairs.

“Controlling our border and preventing illegal immigration is a serious issue, but his insistence that Mexico will fund a wall on the southern border inflames unhelpful passions, and rests on an utter misreading of, and contempt for, our southern neighbor,” the letter says.

Former Bush administration State Department official Eliot Cohen and Bryan McGrath, who advised Mitt Romney’s 2012 campaign, organized the letter, according to the Washington Post. Signatories include former homeland security secretary Michael Chertoff, former Bush homeland security adviser Frances Townsend, and former deputy secretary of state Robert Zoellick.

The foreign policy experts agreed that they would be “unable to support a party ticket with Mr. Trump at its head.” But it’s not clear how much of an impact, if any, the letter would have. As the Post notes, the list of elite, DC-insiders are unlikely to impress Trump supporters who chafe at the Republican establishment’s opposition to the frontrunner.

Fortune has reached out to the Trump campaign and will update this post will their reply.