The ideas that Donald Trump is putting forward are dangerous to America and what his speech on April 27 revealed to me is that he is a dangerous leader.

He doesn’t appear to have the in-depth knowledge—about the world, history, economics, politics—that any serious presidential candidate should have. He lacks the nuance and sophistication that, say, Dwight D. Eisenhower and George H.W. Bush—just to single out two Republican Presidents in the last 50 years—had.

It is that maturity and judgment that are so important in the Oval Office that all of our presidents have to have. He doesn’t appear to have any of it.

Trump’s speech was a categorical denunciation of all of American foreign policy since the end of the Cold War. He said it was a series of failures. He said he was the only person—his words, not mine—who could turn the situation around. He, in effect, indicted all of our past presidents, Republicans and Democrats, since the end of the Cold War, all of our secretaries of state and secretaries of defense.

It takes someone with a very big ego, and probably someone who is very naïve and doesn’t understand global politics, to make such a categorical judgment. The speech was a series of threats and ultimatums.

Donald Trump's Foreign Policy Speech: Three Key Shifts

He appeared in the speech, and in the past several weeks on the campaign trail, to be much tougher on our democratic allies—Britain, France, Germany, Japan, South Korea—than on Russia or China. That obviously is a major miscalculation on his part.

And, finally, he made a major appeal that the United States devote itself to diplomacy. As someone who served in the United States Foreign Service, I certainly support diplomacy. But he is the guy who offended 1.6 billion Muslims and Mexico and our allies with all of his egregious statements, so you have to wonder what kind of diplomacy he is talking about.

Donald Trump says “American First” would be the banner that he would raise. He may want to rethink that. The America First movement of the late 1930s and early 1940s, up until Pearl Harbor, was the American isolationist and appeasement movement that argued that we should not support Britain and France, that we should not support the struggle against Hitler and Nazi Germany. It’s a shameful organization from that period.

To call yourself “America First” indicates that he is unaware of this history or doesn’t care. It is indicative of the campaign that they don’t seem to understand this very important episode of American history.

R. Nicholas Burns is a former U.S. diplomat who served as Under Secretary of State for Political Affairs under President George W. Bush and currently is a visiting fellow at the Hoover Institution at Stanford University. These remarks are an excerpt of an interview he gave the Atlantic Council after GOP frontrunner Donald Trump’s speech on foreign policy on Wednesday.