After last weekend’s Islamist-inspired terror attacks in New York City, New Jersey, and Minnesota, President Barack Obama declared: “As Americans, we will not give into fear.”

That statement places him in one wing of the liberal tradition. Unfortunately, he doesn’t share all of the tradition.

Following sudden and unexpected assaults, presidents of all ideological stripes typically call on the public not to be afraid. The tradition, as historian Matthew Dallek shows in a fascinating new book, “Defenseless Under The Night: The Roosevelt Years and the Origins of Homeland Security,” goes back to the fear Americans felt in the 1930s.

Franklin Roosevelt was the first president to recognize that, in a modern media age, one of his jobs was to be the cheerleader to the nation. As he famously put it in response to the Great Depression, “The only thing we have to fear is fear itself.”

But with the advance of imperial Japan, Nazi Germany, and fascist Italy, many Americans began to entertain new fears — of the rise of fascism, of an attack from the air by bombers, of fifth columnists within. The unexpected collapse of France in 1940 only heightened this fear.

True, the reasons for concern were exaggerated. Nazi bombers couldn’t reach the United States in 1940, and there were no Nazi terror cells in the United States. But the fear was real, and in a wider picture, there was good reason for it: Hitler hated the United States, and a world dominated by totalitarianism would have been a perilous one for American liberty.

This fear elicited two liberal responses. One, led by first lady Eleanor Roosevelt, argued that the United States needed to couple preparations for war abroad with reform at home. The other, led by New York City Mayor Fiorello La Guardia, emphasized war abroad and homeland security.

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La Guardia was just as much a reformer as Roosevelt. And he wanted to fight abroad as much as he wanted fire wardens at home. But he believed the way to meet fascist force was with American force. The first lady didn’t disagree. She just wanted day care at home, too.

Both the mayor and the first lady shared the fears of many Americans. La Guardia regarded fear as useful for mobilizing the American people, while Roosevelt — more wisely — urged Americans to act as if they weren’t afraid. But both wanted the United States to act, to meet the fascist challenge abroad.

In some respects, President Obama fits into the liberal tradition of Eleanor Roosevelt. He’s repeatedly called for “nation-building at home.” He’s enthusiastically promoted what he considers to be domestic reforms. And he’s a great verbal campaigner against fear.

But for Roosevelt, reform was also about the war effort. Day care, for example, would allow women to work in factories while men joined the armed forces. Of course, she would have wanted day care anyhow. But she sincerely believed her reforms would contribute to the war.

And that’s where President Obama falls out of the liberal tradition. Unlike Eleanor Roosevelt, he’s deeply reluctant to use the U.S. military in combat. Instead, he wants the United States to withdraw from foreign conflicts as quickly and fully as possible.

From arguing that firearms are more dangerous than terrorism, to his assertion after the latest attacks that ISIS is on the road to defeat, to his unwillingness to even describe these attacks as terrorism, President Obama doesn’t warn against fear so we can act with courage abroad. He wants us not to be afraid so we won’t feel compelled to get involved abroad.

I don’t pretend there are easy answers to terrorism. There weren’t easy answers to fascism in 1940 either. And true, these threats aren’t the same. But today, as in 1940, there are, serious reasons for us to engage the enemy. Unfortunately, unlike Eleanor Roosevelt and Fiorello La Guardia, President Obama prefers to minimize the threat.

Ted R. Bromund is a senior research fellow in The Heritage Foundation’s Thatcher Center for Freedom.