“Great nations do not fight endless wars,” President Trump declared in his State of the Union address. It was a line that could have been delivered by President Barack Obama, who in 2015 memorably said, “I do not support the idea of endless war.”

Just a few days before Trump’s address, his own party delivered the president a stinging rebuke when Senate Republicans passed a resolution opposing his Syrian and Afghan withdrawals by an overwhelming bipartisan 68-to-23 vote. Trump’s defenders say: That’s just the foreign policy establishment advocating “forever war.” When, they ask, will these wars end? When will we be able to declare victory and go home?

These are fair questions, and they deserve serious answers.

In traditional wars, defining victory is easy. Victory comes when the enemy surrenders and lays down its arms. But this is not traditional war. We are not fighting nation-states with defined borders and armies, navies and air forces. We are fighting radical Islamist terrorists who are engaged in what Osama bin Laden called “a war of destiny between infidelity and Islam.” There will be no signing ceremony on the deck of the U.S.S. Missouri. They will never lay down their arms. In this war, victory for the United States is every day that passes without a terrorist attack on American soil. And that daily victory is made possible because the men and women of the U.S. military are hunting the enemy in faraway lands.

America’s enemies have a very clear definition of victory. For them, victory comes when we give up the fight before they do. We know this because they have told us so. The 9/11 mastermind Khalid Sheikh Mohammed told his CIA interrogator “Americans don’t realize we do not need to defeat you militarily; we only need to fight long enough for you to defeat yourself by quitting.” That is how the terrorists see Obama’s withdrawal from Iraq in 2011 and Trump’s planned withdrawals from Syria and Afghanistan: America defeating itself by quitting.

It is understandable that, after 18 years, Americans want the war to end. But what we want is irrelevant. We don’t get to decide unilaterally that the war is over. The enemy gets a vote. Just because we have tired of fighting doesn’t mean that they have.

Here is the hard truth: We don’t get to choose when the war ends, but we do get to choose where it is fought. It can either be fought over there, in the deserts of Syria and the mountains of Afghanistan, or it can be fought over here — on American streets and in American cities, as it was on Sept. 11, 2001. It’s up to us.

Trump deserves enormous credit for taking the gloves off in the fight against the terrorists. He was absolutely correct when he declared in the State of the Union address, “When I took office, ISIS controlled more than 20,000 square miles in Iraq and Syria. Today, we have liberated virtually all of that territory from the grip of these bloodthirsty monsters.” But the Islamic State is not defeated. It still has tens of thousands of fighters under arms and, according to one estimate by the Institute for the Study of War, as much as $400 million it smuggled out of Iraq, money that can be used to sustain its movement and plan attacks across the world.

In Afghanistan, U.S. intelligence estimates there are about 20 terrorist groups — including al-Qaeda and the Islamic State affiliate known as Islamic State Khorasan, or IS-K — who would immediately gain an uncontested sanctuary from which to plan new attacks if America withdraws. On Jan. 28, the New York Times reported that a 2017 intelligence assessment, renewed last year, “says a complete withdrawal of American troops from Afghanistan would lead to an attack on the United States within two years.”

Right now, the U.S. military has its boot on the terrorists’ necks. They are focused on survival, not on launching faraway attacks. Take that boot away, though, and the terrorists will get up, dust themselves off, regroup, rebuild and go back to trying to kill Americans in the United States.

In his address, Trump praised the heroism of the men who stormed the beaches of Normandy on D-Day. “They did not know if they would survive the hour,” he said. “They did not know if they would grow old. But they knew that America had to prevail.”

The same is true today. Great nations do not quit before they prevail.

Marc Thiessen is a columnist with The Washington Post. Follow him on Twitter, @marcthiessen.

Marc Thiessen