In a national security presidential memorandum signed on January 27, U.S. President Donald Trump promised “a new Nuclear Posture Review to ensure that the United States’ nuclear deterrent is modern, robust, flexible, resilient, ready, and appropriately tailored to deter 21st-century threats and reassure our allies.” This statement on nuclear policy marks a drastic change from President Barack Obama’s call to “reduce reliance” on nuclear weapons while maintaining a “safe, secure, and effective,” nuclear force.

The move will be contentious. As Amy Woolf of the Congressional Research Service writes, this may be the first post–Cold War U.S. administration not to seek a reduced role for nuclear weapons as an explicit policy objective. Among the most highly debated aspects will be the decision, also articulated in Secretary of Defense James Mattis’ confirmation hearings earlier this month, to upgrade all three legs of the U.S. nuclear triad: bombers, submarines, and intercontinental ballistic missiles (ICBMs).

Such modernization plans have been the subject of intense controversy in recent years. In 2010, the Obama administration agreed, under Republican pressure, to update the country’s aging nuclear forces, but the decision provoked a withering response, with particular criticism aimed at ICBMs. Writing in Foreign Affairs, for example, journalist Fred Kaplan argued that “the case for land-based ICBMs today is extremely weak” and asked rhetorically, “Why shouldn’t they be dismantled?” Former Secretary of Defense William Perry answered the question in a New York Times op-ed, explaining “Why It Is Safe to Scrap America’s ICBMs.” He argued that doing so could save “considerable costs” and reduce the risk of “accidental nuclear war.” And in a Senate testimony in 2015, Mattis himself suggested he was open to the possibility, inquiring, “Is it time to reduce the triad to a dyad, removing the land‐based missiles?”

This is a valid question to ask, but in a world of growing nuclear dangers, the Trump administration is correct: the United States must retain a robust nuclear force, including ICBMs.

The primary purpose of the United States’ nuclear weapons is to deter an enemy nuclear attack, and ICBMs are central to that mission. To launch a devastating nuclear first strike on the United States, an adversary would need to target at least 455 sites on the U.S. mainland (450 ICBM silos, three bomber bases, and two submarine bases). That would be a daunting, if not impossible, task. Subtract the ICBMs from this equation, however, and the opening ante for a nuclear attack on the United States plummets to only five sites. With a target set this small, even a minimally armed rogue state such as North Korea might be enticed to take a nuclear pot shot.

Moreover, the United States not only aims to deter attacks on itself, it also extends deterrence to over 30 allies in Europe and Asia. Here, once again, ICBMs are critical for mission success. Unlike the other legs of the triad, ICBMs can hit any target on Earth in 30 minutes or less. This swift global reach is an important aspect of the global nuclear umbrella. Indeed, during a trip to Tokyo in December, Japanese experts told me that the ICBMs were particularly reassuring in the face of growing North Korean threats.

Finally, ICBMs can save millions of American lives. At present, U.S. rivals such as Russia likely target a large portion of their nuclear weapons against remote ICBM fields in Montana, North Dakota, and Wyoming. Moscow would want to destroy as many of our nuclear weapons as possible in a first blow, to prevent us from using them against the Russian homeland in retaliation. If these missiles did not exist, Moscow would likely target freed-up nuclear forces against U.S. cities instead. The dismantling of the ICBMs would, therefore, in the event of a nuclear war, increase the number of American casualties by approximately 50 million, according to my estimate.

For all these substantial benefits, critics nevertheless cite several reasons to jettison ICBMs. Beyond the idea that the other legs are sufficient for deterrence, they maintain that cutting ICBMs is fiscally prudent, given Washington’s plans to spend $1 trillion over the coming 30 years to modernize all three legs of the triad. Granted, a trillion dollars is no small sum, but the full cost of nuclear modernization is only about five percent of the U.S. defense budget, which is a bargain considering what the country gets in return. Finally, critics assert that ICBMs are destabilizing. They worry that, in a crisis, a U.S. president would want to launch ICBMs before they could be destroyed. Therefore, a president might launch nuclear weapons in response to a false alarm.

At first blush, this last argument may seem persuasive, but it contains a logical fallacy: If a president would be so worried about an enemy eliminating the United States’ ICBMs that he might start a nuclear war over it, then why would the United States eliminate ICBMs itself? This is like advocating suicide to prevent murder. Moreover, this criticism misses the logic of deterrence. As long as the country retains a robust nuclear force, it is unlikely that a president will ever face this dilemma. As Mattis put it, “What we’re trying to do is set such a stance with our triad that these weapons must never be used.”

It would certainly be nice if conditions permitted the United States to cut its nuclear weapons, but with growing North Korean nuclear threats, increasing military competition with a nuclear-armed China, and renewed Russian nuclear sabre rattling, the Trump administration’s decision to continue with plans to modernize all three legs of the U.S. nuclear triad should be celebrated. As former Secretary of Defense Ash Carter put it last year, speaking just steps from a missile field in North Dakota, the nuclear triad remains “the bedrock of our security.”