President Trump has authorized a plan to cut 9,500 of the 34,500 U.S. troops stationed in Germany — news that blindsided the German government on Friday night. The plan will also cap the number of U.S. troops deployed in Germany at 25,000.

Germany, a longtime member of the NATO alliance, hosts more than half of all U.S. troops deployed to Europe. The U.S. withdrawal plan comes after repeated rows with Germany over its defense spending and follows a recent decision by German Chancellor Angela Merkel not to travel to the United States for a Group of Seven meeting.

But this move is also consistent with Trump’s long-standing antipathy to American alliances. Here are five reasons why it matters.

1. U.S. troops aren’t there simply to aid Germany

As I show in my new book, “Shields of the Republic: The Triumph and Peril of America’s Alliances,” the United States formed defense treaties and stationed troops abroad after World War II for the sake of self-defense. By working together, the United States and its allies would dissuade the Soviet Union and its allies from attacking them and be better prepared to defend Europe if they did.

The U.S. strategy was a new one — countries had long used alliances to fight wars, but Washington’s goal was to keep them from starting. By most measures, the alliance system was a resounding success. No U.S. ally was ever the victim of an unprovoked Soviet attack, and the United States hasn’t been dragged into wars on its allies’ behalf. NATO has invoked Article V, the principle of collective defense, only once — following the Sept. 11, 2001, terrorist attacks on the United States.

During the Cold War, a divided Germany served as the front line. Currently, up to 50,000 American troops may be deployed to U.S. bases in Germany as part of NATO’s defense of the European continent, primarily against Russia. Germany also hosts U.S. Africa Command, major military hospitals and training facilities that enable other U.S. military activities worldwide.

2. The move isn’t likely to boost German defense spending

The Trump administration has criticized Germany repeatedly for its low defense spending levels. As Jim Goldgeier has shown here at TMC, such criticisms started well before Trump.

But cutting U.S. troops is unlikely to improve the burden-sharing balance between Washington and Berlin. Like other NATO members, Germany pledged to increase its defense spending to 2 percent of GDP in 2014; it is not on track to meet that target by 2024. German defense spending has grown as an absolute value, but so has its economy. It also spends in ways that aren’t terribly efficient for the alliance, devoting a high percentage of its defense budget to personnel costs as opposed to equipment or research and development.

There is also no reason to think the threatened withdrawal will coerce Merkel into spending more. Merkel is popular at home, particularly since leading one of the world’s most effective pandemic responses — and she plans to leave office in 2021. Instead, the U.S. troop drawdown may energize a German opposition party that already favors reducing integration with NATO.

3. The troop withdrawal will cost the United States — in multiple ways

Withdrawing troops from Germany means the United States must still pay the costs of supporting them somewhere. But the United States will also have to pay the bill for repatriating or relocating them to other countries, as well as shuttering facilities in Germany. Relocating U.S. troops to Poland, for instance, would involve significant new costs to build facilities in Poland.

But here’s the added cost to the United States: military readiness. NATO’s most urgent military mission is the defense of its eastern flank — in particular, the Baltic states. Since Russia’s 2014 annexation of Crimea and invasion of Ukraine, NATO has focused on improving its readiness, should Russia attempt a fait accompli grab in the Baltics and try to seize a swath of territory before the alliance can arrive to defend it.

Depending on where the troops are sent, the withdrawal in Germany could reduce NATO’s readiness, making conditions more favorable for a Russian advance — but also aids Russia’s national strategy to erode NATO cohesion. If Russian President Vladimir Putin attempts a land grab and the United States is drawn into conflict or crisis later, the U.S. cost — in both blood and treasure — will be far higher than the price tag to make sure NATO can prevent such a conflict from starting.

4. The drawdown may have implications for other alliances

The Trump administration also has threatened to draw down U.S. troops in South Korea and Japan, arguing that the United States pays more than its fair share of the defense bill.

Because of the support they already provide for the U.S. presence, South Korea and Japan are the cheapest places in the world to base U.S. troops. Yet the Trump administration and South Korea have been locked in a cost-sharing standoff since the United States demanded that South Korea quintuple its financial support for the alliance.

South Korean negotiators have made concessions to U.S. demands, but the talks remain deadlocked, which caused the United States to furlough 4,000 South Korean staff from American bases at the height of the pandemic. Despite the growing nuclear and missile threat from North Korea, Trump has repeatedly threatened to withdraw troops from South Korea, and had linked the spending talks to troop levels. The United States and Japan are due to renegotiate their cost-sharing arrangements next year.

5. There are few checks on the president’s power to execute this plan

The Senate must advise and consent to alliance treaties when they are formed, but it has minimal power over a president’s alliance management decisions once a treaty is in force.

There are few checks on the president’s ability to adjust troop deployments to allied territory. In 1977, Congress thwarted an effort by President Jimmy Carter to draw down U.S. troops from Korea by passing a bill that required the president to involve the legislature in future withdrawal decisions. In December, Congress passed a bill that requires the secretary of defense’s sign-off on any drawdown from South Korea.

Congress could attempt to slow the withdrawal from Germany by refusing to appropriate funds associated with troop relocation. But whatever Congress does in response, the Trump administration will probably try to sell this withdrawal as a money-saving move. For the United States, however, the net result will probably be higher costs.

Mira Rapp-Hooper (@MiraRappHooper) is Steven Schwarzman Senior Fellow for Asia Studies at the Council on Foreign Relations and the author of “Shields of the Republic: The Triumph and Peril of America’s Alliances” (Harvard University Press, 2020).