Homeland Security Secretary Jeh Johnson has a message for Americans panicking over terrorist attacks, cyberespionage, and undocumented immigrants coming across the border: Calm down, and get some perspective.

“We must recognize that our first impulse in reaction to a threat to the American people is often not the best one,” Johnson said in a prepared speech Wednesday at Westminster College in Fulton, Missouri.

“I can build you a perfectly safe city, but it will amount to a prison,” he continued.

“I can guarantee you a commercial air flight perfectly free from the risk of terrorist attack, but all the passengers will be forced to wear nothing but hospital-like paper smocks, and not be allowed any luggage, food, or the ability to get up from their seats.…”

“I can guarantee you an email system perfectly free from the risk of cyberattack, but it will be an isolated, walled-off system of about 10 people, with no link to the larger, interconnected world of the Internet.”

In remarkably candid language, Johnson offered a broad critique of U.S. security measures, many of which are implemented by his own department, the third-largest in the federal government with an annual budget of $60 billion and 225,000 employees.

“Given all this, there are a lot of ways in which DHS can potentially assert itself in the daily lives of the American public, in the name of homeland security,” Johnson said.

“But, as secretary of this large department with all its resources, I know we must guard against the dangers of overreaction in the name of homeland security. It’s not simply a matter of imposing on the public as much security as our resources will permit.”

Johnson could have hardly picked a more appropriate place to haul out the big rhetorical guns. It was at Westminster College that Winston Churchill delivered his famous “Iron Curtain” speech in 1946. And in 1954, Harry S. Truman opined there on the dangers of “witch-hunting and hysteria” during the frantic days of the Red Scare and the fear of rising communism.

“That is the inspiration for my remarks here today,” Johnson said of Truman’s speech. “In his usual plain and blunt language, Truman rebuked the specter of McCarthyism with the words, the ‘descendants of the ancient order of witch-hunters have learned nothing from history.’ He went on to say ‘[t]he cause of freedom both at home and abroad is damaged when a great country yields to hysteria.’”

That a sitting secretary of homeland security would draw a line between the “hysteria” of Cold War America and the post-9/11 security state could be called an act of commendable courage or profoundly impolitic—or both.

But Johnson spoke with the benefit of some history. It’s been 14 years since the 2001 terrorist attacks that gave rise to his department, plenty of time to take an honest assessment about the strengths and weaknesses of the choices the country has made.

And he recalled the experience of his own grandfather, Charles S. Johnson, a president of Fisk University in Nashville from the mid-1940s to the mid-1950s and an outspoken critic of the Red Scare. Johnson testified before the notorious House Un-American Activities Committee to deny allegations that black colleges had been infiltrated by communists, his grandson said.

The college president had hired a white math professor who couldn’t get a job because of his suspected communist links. In 1955, under pressure, Johnson was ultimately forced to dismiss the man, a decision that the secretary said may have contributed to his grandfather’s sudden death, at the age of 63, from a massive heart attack.

Johnson was clearly hearing the ghosts of history—America’s and his own.

“I can profile people in this country based on their religion, but that would be unlawful and un-American,” he said.

“We can erect more walls, install more screening devices, and make everybody suspicious of each other, but we should not do so at the cost of who we are as a nation of people who cherish our privacy, our religions, our freedom to speak, travel and associate, and who celebrate our diversity and immigrant heritage.

“In the final analysis, these are the things that constitute our greatest strengths as a nation.”