But it is in the realm of national security and foreign policy that Mr. Trump has truly raised alarm among many Republicans. Dozens of GOP foreign policy experts signed a letter announcing they would not vote Mr. Trump because he would be a "dangerous president" who would "put at risk our country's security and well-being." Not only does he lack experience in foreign policy, they wrote, but he "shows no interest in educating himself." No less a conservative than Paul Wolfowitz, one of the Bush administration's chief proponents of the Iraq war, observed of Mr. Trump, "He says he admires [Vladimir] Putin, that Saddam Hussein was killing terrorists, that the Chinese were impressive because they were tough on Tiananmen Square. That is pretty disturbing." He added: "The only way you can be comfortable about Trump's foreign policy is to think he doesn't really mean anything he says."