THE US has about 46,000 troops stationed in 11 countries across the Middle East, with all the accompanying hardware and support. Those forces are not available elsewhere, whether in Europe or East Asia, where America’s most ominous foes need deterring, and its closest allies need reassuring. One of the biggest strategic questions for US President Joe Biden — or Donald Trump if he wins in November — is whether to maintain this huge American presence or draw it down.

Right now would be the wrong time for such a drastic change. America is consumed by partisan acrimony in the run-up to its election. Israel is waging war in the Gaza Strip and stands accused of genocide. And Iran-backed militias from Yemen to the Levant have not only the Zionists but also US troops in their crosshairs. One such group killed three Americans with a drone strike on a US base in Jordan just the other day. If the US were to pull out now, it would hand Tehran a propaganda victory and risk chaos reminiscent of 2021, when Biden fecklessly abandoned Afghanistan.

But what about the medium term? At some point this year, the hot phase of Israel’s campaign against Hamas will end. Iran and its proxies may, after Biden’s retaliation this month for the three dead Americans, refrain from major escalation against US forces. And by the end of the year, fingers crossed, Americans may know who’ll be in the White House for the next four years.

What makes the US presence in the Middle East especially relevant is that it’s also the prime case study in a larger debate about America’s role in the world. Should the US remain a hegemon, using its leadership to preserve a modicum of global order? Or should it retrench to deal with its own problems, leaving an increasingly multipolar and anarchical world to unrestrained power politics?

I gravitate toward the former camp, also known in Washington as internationalism (as opposed to isolationism). History shows that periods when hegemony is absent or ambiguous (such as the 1920s and 30s) tend to end in disaster (World War II). Even for a hegemon, it’s cheaper in the long run to incur the costs of keeping order than to clean up the messes of global calamity.

But even internationalists need to accept that hegemony cannot mean that the US must be active everywhere all the time. Christopher Preble at the Stimson Center, a think tank in Washington, argues that the US has already lost global “primacy” and can’t afford to get it back. During the last two decades of the Cold War, for example, US public debt averaged 38% of economic output; last year, it ran to three times that ratio. Americans increasingly want their country to invest in solving problems at home, and to set clear priorities abroad.

Is the Middle East such a priority? My colleague Hal Brands argues that the history of failed American attempts to exit the region proves its geopolitical centrality and means that the US must stay because “such is the burden of a hegemon.”

Others beg to differ. Daniel Depetris at Defense Priorities, another Washington think tank, thinks the US should withdraw its roughly 3,400 military personnel in Iraq and Syria as soon as possible, and eventually also the tens of thousands in the Gulf states and the rest of the region.

That’s because the US troops have completed their ostensible mission of the past decade, which has been to destroy the Islamic State, a barbaric terrorist group that formed in the aftermath of America’s ill-considered second war against Iraq. Today, the Islamic State no longer controls any territory and has been degraded to a point where its regional foes, from Syrian Kurds to Shia fighters, can keep it subdued without US help.

Other more expansive justifications for a US presence are iffy, Depetris argues. For example, the US, a net exporter of oil nowadays, relies much less on hydrocarbons from the Gulf region than it did during the oil shocks of the 1970s, and world markets have become more resilient too. Over time, the Western economies will supposedly wean themselves from fossil fuels anyway. So if Iran tried to close the Strait of Hormuz, it would hurt its own customers, notably China. In any case, the US and its allies can intervene to keep trade routes open even without a permanent presence.

Some strategists want the Americans to stay in order to prevent Iran from becoming a regional hegemon. But Iran is nowhere near as militarily dominant in its neighborhood as Russia and China are in theirs. Besides, the region’s other powers, notably Saudi Arabia and Turkey, would organize constellations to counter Tehran’s weight. The US can support such efforts by building alliances — Turkey is already a NATO member, and Washington is in talks with Riyadh about mutual security guarantees.

The idea that an American exit would create a vacuum that Moscow or Beijing would step into is also overblown. Russia dabbles in Syria, Africa, and elsewhere, but it’s mainly trying to project its power into eastern Europe and central Asia, as well as the Arctic. China is eyeing the Taiwan Strait and the East and South China Seas. A US withdrawal wouldn’t hand the Middle East to the Kremlin or Zhongnanhai just as the US retreat from Vietnam didn’t give them Southeast Asia.

The strategic downsides of the US presence are clearer. As Kelly Grieco, also at the Stimson Center, argues, the Americans in the Middle East, instead of deterring Iran and its proxies, serve as provocations and targets, breeding anti-Americanism and terrorism. The recurrent need for the US to retaliate tit-for-tat against low-level attacks raises the risk of unintended escalation drawing the US into a major war that it and the world don’t need.

Moreover, Washington, by deploying its own strength, actually encourages its partners, such as Riyadh, to free-ride and do less than they can for regional security. As it happens, neo-isolationists also use this argument to demand more US “restraint” in Europe and East Asia.

Does the American defense umbrella not tempt Japan, say, to spend less than it otherwise would to protect itself against China and North Korea? Does Germany not shirk its duties in the transatlantic alliance against Russia? Trump taps into American frustration at such perceived free-riding, claiming that he would encourage the Russians to do “whatever the hell they want” to Washington’s European allies who skimp on their armies.

Washington must indeed manage the moral hazard that comes with American alliances. And there are positive signs already. Tokyo just passed its largest ever military budget, and Berlin has set up a special fund to boost its defense spending.

But there are also huge differences between the US commitments in Europe and East Asia and those in the Middle East. By invading the sovereign country of Ukraine and threatening Moldova and others, Russia has brought naked imperialist aggression back to Europe. And by threatening Taiwan and the countries around the South China Sea, China has thrown its revanchist gauntlet at the entire “rules-based” international order. Russia has the world’s largest arsenal of nuclear weapons; China has the third largest and entertains ambitions for parity with Russia and the US. If there is ever, heaven forbid, a World War III, it will be between the US and one or both of these autocracies.

By contrast, neither the tragic 75-year-old conflict between Israelis and Palestinians nor the 45-year quest by Iran’s theocracy for regional dominance needs to escalate into a global conflagration. Israel, with the region’s strongest army and its only nuclear arsenal, can defend itself. Iran is best dissuaded from building its own nukes, but could be deterred by Israel much as India and Pakistan hold each other in check. In time, it’s up to the peoples of the Middle East to make peace, and no outside power can force them.

What the debate about the US presence in the Middle East boils down to is opportunity cost. An American soldier standing guard at Tower 22 in the Jordanian desert cannot simultaneously watch over the NATO border in Estonia, the demilitarized zone on the Korean peninsula or Philippine shoals in the South China Sea. Captain America has a shield that’s big but not global. To keep holding it over Europe and East Asia, he must withdraw it from the Middle East.

BLOOMBERG OPINION