President Donald Trump plans to withdraw the US military contingent stationed in northeast Syria. This may be implemented slowly, but the US troops eventually will be brought home. Trump’s disengagement from Syria and Iraq is in sync with American attempts to reach an understanding with the Taliban that will allow an honorable US withdrawal from Afghanistan as well.Those foreign policy decisions seem to constitute a part of a larger trend to reduce US involvement in the Middle East, a trend that began during the tenure of president Barack Obama. This reflects weariness of foreign involvements, a weariness engendered by US involvement in two unsuccessful wars (Iraq and Afghanistan). Reinforcing this is the diminishing importance of the oil-rich Middle East to the US. American focus on the Chinese challenge also reinforces this. In addition, Trump’s isolationist impulses play a role in lowering America’s military profile abroad.The withdrawal of American forces may have strategic merits. The rationale for a contracted global military seems to match what American strategists have called an “offshore balancing” posture. This means that the US will hold fewer overseas bases but nevertheless maintain the military capability to intervene in distant areas. In this way, American forces will be less vulnerable to the whims and provocations of regional actors and used only when vital American interests are at stake.Yet the adoption of an “offshore balancing strategy” commensurate with a superpower status requires a US military force buildup to project power far away. Without such a buildup, the US will lack credible deterrence.Unfortunately, the US military is in poor shape, and at present cannot sustain such a posture. The US defense budget peaked in fiscal year 2010 and then declined during the Obama administration. The budget bottomed out in fiscal year 2016 and has been climbing somewhat since then.It’s true that the Obama administration’s planned cuts have been reversed, given Russian aggression (the occupation of Crimea), the rise of ISIS and a newly assertive China (which is expanding its hold on the South China Sea). But even under Trump, defense outlays are flat (after deducting for inflation). The House of Representatives (which is controlled by the Democratic Party) is unlikely to support further defense expenditures.The two branches of the military that must carry the weight of an offshore balancing strategy – the air force and the navy – are in particularly bad shape.The readiness of US Air Force aircraft is on a multiyear slide. The overall mission-capable rate for its aging fleet of aircraft dropped below 70% in 2018 – its lowest point since 2012. This means that fewer than seven out of 10 planes are ready to perform their designated missions at any given time.The US Navy is aging, too. The navy is considering extending the service life of all its ships by at least seven years, and it could stretch the life of some ships by 13 years. This means that some active ships could be as much as 53 years old, hardly fit for achieving their mission.Redressing this situation will take time and considerable amounts of money. In the meantime, the US is a superpower in decline, suffering from a loss of capabilities and direction.THE ONLY way to prevent further decline in American capabilities, particularly in the Middle East, is to bolster deterrence. A withdrawal from the Middle East must be accompanied by steps that reduce the general impression of a weak US going home in defeat.The place to make a stand is regarding Iran. Obama cut a deal with Iran that only encouraged its quest for hegemony and drive for nuclear weapons, while buying time in the hope that Iran will not harass the United States. In contrast, Trump understands that the Islamic Republic of Iran is an enemy of the US and that it is determined to acquire a nuclear weapon. But his hopes for forcing Iran to change its policies under diplomatic and economic pressure, while pursuing a policy of US disengagement from the Middle East, are unlikely to be realized.The only way to leave the Middle East with as little as possible damage to US standing and security is to leave with a big bang. Washington must instill fear in the hearts of its enemies.Despite the significant reduction in American military capabilities, the US still has enough punch to punish regional opponents and to generate fear. The US still possesses a strong enough air force to conduct a short campaign to destroy the critical Iranian nuclear installations.Such military action would also delay nuclear proliferation, an important goal for the US, encourage US regional allies and discourage its opponents.Indeed, action against a nuclear-aspiring Islamist Iran would reverberate beyond the Middle East and send a clear signal to anti-American forces all over the world.Enhanced deterrence would prevent further Iranian provocations and would buy the US time to put its house in order and get serious about being a superpower.The writer, a professor, is president of the Jerusalem Institute for Strategy and Security (jiss.org.il) and a fellow at the Middle East Forum.