This is a column directed at high school and college students. I’m going to try to convey to you how astoundingly different the Republican Party felt when I was your age.

The big guy then was Ronald Reagan. Temperamentally, though not politically, Reagan was heir to the two Roosevelts. He inherited a love of audacity from T.R. and optimism and charm from F.D.R.

He had a sunny faith in America’s destiny and in America’s ability to bend global history toward freedom. He had a sunny faith in the free market to deliver prosperity to all. He had a sunny faith in the power of technology to deliver bounty and even protect us from nuclear missiles.

He could be very hard on big government or the Soviet Union, but he generally saw the world as a welcoming place; he looked for the good news in others and saw the arc of history bending toward progress.

When he erred it was often on the utopian side of things, believing that tax cuts could pay for themselves, believing that he and Mikhail Gorbachev could shed history and eliminate all nuclear weapons.

The mood of the party is so different today. Donald Trump expressed the party’s new mood to David Muir of ABC, when asked about his decision to suspend immigration from some Muslim countries: “The world is a mess. The world is as angry as it gets. What, you think this is going to cause a little more anger? The world is an angry place.”

Consider the tenor of Trump’s first week in office. It’s all about threat perception. He has made moves to build a wall against the Mexican threat, to build barriers against the Muslim threat, to end a trade deal with Asia to fight the foreign economic threat, to build black site torture chambers against the terrorist threat.

Trump is on his political honeymoon, which should be a moment of joy and promise. But he seems to suffer from an angry form of anhedonia, the inability to experience happiness. Instead of savoring the moment, he’s spent the week in a series of nasty squabbles about his ratings and crowd sizes.

If Reagan’s dominant emotional note was optimism, Trump’s is fear. If Reagan’s optimism was expansive, Trump’s fear propels him to close in: Pull in from Asian entanglements through rejection of the Trans-Pacific Partnership. Pull in from European entanglements by disparaging NATO. It’s not a cowering, timid fear; it’s more a dark, resentful porcupine fear.

We have a word for people who are dominated by fear. We call them cowards. Trump was not a coward in the business or campaign worlds. He could take on enormous debt and had the audacity to appear at televised national debates with no clue what he was talking about. But as president his is a policy of cowardice. On every front, he wants to shrink the country into a shell.

J.R.R. Tolkien once wrote, “A man that flies from his fear may find that he has only taken a shortcut to meet it.”

Desperate to be liked, Trump adopts a combative attitude that makes him unlikable. Terrified of Mexican criminals, he wants to build a wall that will actually lock in more undocumented aliens than it will keep out. Terrified of Muslim terrorists, he embraces the torture policies guaranteed to mobilize terrorists. Terrified that American business can’t compete with Asian business, he closes off a trade deal that would have boosted annual real incomes in the United States by $131 billion, or 0.5 percent of G.D.P. Terrified of Mexican competition, he considers slapping a 20 percent tariff on Mexican goods, even though U.S. exports to Mexico have increased 97 percent since 2005.

Trump has changed the way the Republican Party sees the world. Republicans used to have a basic faith in the dynamism and openness of the free market. Now the party fears openness and competition.

In the summer of 2015, according to a Pew Research Center poll, Republicans said free trade deals had been good for the country by 51 to 39 percent. By the summer of 2016, Republicans said those deals had been bad for America by 61 percent to 32 percent.

It’s not that the deals had changed, or reality. It was that Donald Trump became the Republican nominee and his dark fearfulness became the party’s dark fearfulness. In this case fear is not a reaction to the world. It is a way of seeing the world. It propels your reactions to the world.

As Reagan came to office he faced refugee crises, with suffering families coming in from Cuba, Vietnam and Cambodia. Filled with optimism and confidence, Reagan vowed, “We shall seek new ways to integrate refugees into our society,” and he delivered on that promise.

Trump faces a refugee crisis from Syria. And though no Syrian-American has ever committed an act of terrorism on American soil, Trump’s response is fear. Shut them out.

Students, the party didn’t used to be this way. A mean wind is blowing.