NEW YORK — President Trump is already pulling U.S. troops out of Syria, and is likely to pull them out of Afghanistan, too, assuming that a tentative peace deal with the Taliban is finalized. Although Trump initially claimed the United States had won in Syria, the real impetus for both moves is a widespread sense that not only aren't we winning, but that we can't possibly win these "forever wars."

"There is virtually no possibility of a military victory over the Taliban and little chance of leaving behind a self-sustaining democracy," wrote strategist and travel writer Robert D. Kaplan in the New York Times. Veteran diplomats Aaron David Miller and Richard Sokolsky, meanwhile, wrote for NPR that "ISIS isn't Germany or Japan, where the U.S. and its allies broke those regimes' will to fight, destroyed all their war-making capacity, eradicated their fascist state ideologies and helped reshape a new environment for two democratic countries. For the U.S. to achieve that goal in Syria is mission impossible."

I have enormous respect for these writers, but their observations, while true, are also irrelevant. James Dobbins, a former U.S. envoy to Afghanistan and Pakistan, and his colleagues at Rand are closer to the mark when they write: "Winning may not be an available option, but losing certainly is. A precipitous departure, no matter how rationalized, will mean choosing to lose. The result would be a blow to American credibility, the weakening of deterrence and the value of U.S. reassurance elsewhere, an increased terrorist threat emanating from the Afghan region, and the distinct possibility of a necessary return there under worse conditions."

The Rand report is about Afghanistan, but the same analysis applies to Syria.

Neither the Islamic State nor the Taliban are remotely defeated. The Islamic State has lost virtually all of its "caliphate," but Director of National Intelligence Daniel Coats just warned that it "still commands thousands of fighters in Iraq and Syria, and it maintains eight branches, more than a dozen networks, and thousands of dispersed supporters around the world."

The Taliban are doing even better: They control or contest 44 percent of Afghanistan's districts, and they are inflicting heavy casualties on Afghan security forces. If the United States pulls out of Afghanistan, the Taliban is likely to seize most of the country, and if we pull out of Syria, the Islamic State is likely to revive.

In fighting these insurgents, the United States needs to eschew its big war mindset. Yes, there will be no surrender ceremony on the deck of the USS Missouri. But even victory in World War II would have been squandered as readily as victory in World War I if the United States hadn't kept troops in Europe and Asia for 73 years and counting.

When U.S. troops pull out, the consequences are usually costly, whether it's the communist takeover of Cambodia, Laos and South Vietnam in 1975, or the rise of the Islamic State after 2011. And, while the Viet Cong weren't trying to attack the American homeland, the Islamic State and al-Qaeda are. The New York Times reports that U.S. intelligence has warned that "a complete withdrawal of U.S. troops from Afghanistan would lead to an attack on the United States within two years."

Advocates of retreat will argue that an open-ended deployment is not sustainable. But that's not true. U.S. troops are volunteers. As long as they aren't taking many casualties, the public isn't opposed to their deployment. U.S. forces have suffered six fatalities in Syria and 66 in Afghanistan since 2015 — an average of 18 a year. Those losses are tragic, but in 2017 the U.S. military lost 80 service personnel in training accidents. Training is now four times deadlier for U.S. forces than combat.

Nor are these conflicts financially ruinous: The war in Afghanistan accounts for less than 10 percent of the defense budget. If Trump chooses to pull out, it will be his choice. He will not have been compelled to exit by public pressure. There are no antiwar protests in the streets.

We need to think of these deployments in much the same way we thought of our Indian Wars, which lasted roughly 300 years (ca. 1600-1890), or as the British thought about their deployment on the North West Frontier (today's Pakistan-Afghanistan border), which lasted 100 years (1840s-1940s). U.S. troops are not undertaking a conventional combat assignment. They are policing the frontiers of the Pax Americana.

Just as the police aren't trying to eliminate crime, so troops are not trying to eliminate terrorism but, instead, to keep it below a critical threshold. This isn't as satisfactory as pursuing unconditional surrender, but, as we may discover before long, it beats the alternative.

Trump is not ending, much less winning, the wars in Syria or Afghanistan. The Taliban's promises of good behavior are worthless, and thr Islamic State doesn't make any promises at all. If Trump brings U.S. troops home, he is choosing to lose — and to squander the military's sacrifices since 2001.

Boot is a Washington Post columnist.