The Trump administration’s budget proposal for 2018 sent shockwaves across the country, but when it came to one slice of the funding, the international-affairs budget, those waves extended across the globe.

The proposed 31 percent cut affects the U.S. bilateral foreign-aid accounts; funding for the United Nations, World Bank, and other international institutions; and the State Department’s diplomatic duties. The United States’ friends and allies in the developing world now have tangible evidence, in place of vague speculation, of what they had most feared since Donald Trump’s election in November: the withdrawal of the United States from active international leadership in the world.

At current levels, the $30 billion U.S. foreign-aid budget is less than 1 percent of the $3.8 trillion federal budget, though polls show Americans believe it takes up a much larger share. Trump’s proposal, which functions as a blueprint of his vision for the government, would cut U.S. aid funding to a level not seen since the 1970s and 1990s. As such, his budget echoes a mistake that other presidents have made: diminishing the power of U.S. foreign aid at a time when it’s crucial to American interests.

The 1970s and 1990s marked the end of two cycles of war: The Vietnam War ended in 1973 and the Cold War ended as the Soviet Empire collapsed in 1991. In both cases, the national-security imperatives facing the United States changed dramatically overnight, and so did the resources for foreign aid. This follows a well-worn pattern: Whenever foreign threats to America’s vital interests rise, so does foreign spending, and whenever those threats appear to diminish, so do aid budgets.

By the time I was sworn in as U.S. Agency for International Development administrator in May 2001, there were just 1,150 USAID Foreign Service officers—the personnel who manage health, agriculture, education, and disaster-relief programs, among others, in developing countries. By contrast, at the peak of Vietnam, there had been more than 12,000. The aid reductions in the 1990s put the United States at a disadvantage into the 2000s. The circumstances that gave rise to the September 11 attacks, for example—al-Qaeda rose out of several fragile and failing states—were best addressed by experienced aid workers and diplomats. But by the time the attacks happened, precious few were left at USAID or the State Department. The Bush administration began to staff up the Foreign Service in 2003, the year the Iraq War began and the first year since Vietnam that there were more officers than there had been the year before.

The post-September 11 USAID-State Department infrastructure that the Trump budget proposes to dismantle deals with the challenges of small wars and crises, and aims to prevent them from becoming regionalized and internationalized. It was designed to address threats that are short of war, but in wartime necessitate a team of State Department and USAID officers ready to serve on the front lines.

Today, the notion that threats to American national-security interests don’t merit a robust foreign-aid program is preposterous. The spread of infectious diseases, such as Ebola and Zika; the threat of radical Islamist terrorist movements across North Africa, which are destabilizing to our friends and allies; the mass-migration crisis that is changing the face of American and European politics; an aggressive and expansionary Russia that’s preying on weak states, such as Ukraine; and the growing number of fragile and failing states are all direct threats to the national-security interests of the United States.

In public, Secretary of State Rex Tillerson has argued that the State Department budget he inherited from the Obama administration was a war budget, and was “unsustainable”—because the United States will be involved in fewer wars in the future, higher aid spending and staffing levels aren’t needed. But how the White House can anticipate future wars is a mystery, as experienced foreign-policy experts over the past century have failed at this task more than they’ve succeeded. Most of the wars of the 20th century, large and small, were not anticipated by anyone, least of all by the U.S. government.

Further complicating the matter, the president has ordered Defense Secretary James Mattis to develop a plan to destroy ISIS. In the unlikely event that it works, and some sort of peace is fashioned in Syria and Iraq, do the United States, Russia, and our allies simply intend to walk away after the military campaign is over and leave behind the wreckage of the war—and the 10.9 million displaced people and refugees to fend for themselves?

In justifying the proposed cuts, the Trump administration has also argued that other wealthy countries should do more. During the campaign and into his early presidency, Trump has made a legitimate point, if inelegantly spoken, that most European states have left their defense to the United States. But using this rationale to explain cuts in the U.S. aid budget makes no sense, because the Europeans, Japanese, and Canadians already contribute much more aid than the United States does. For example, in 2015, the United States ranked 20th out of about 30 donor governments when it came to foreign aid as a percentage of gross domestic product. It is the United States that should be giving more.

The real reason for the proposed aid cuts has to do with American politics. When federal spending must be cut, the least painful reductions politically are in the foreign-affairs budget, because the immediate pain is felt by people who do not vote in American elections. Yet a feast or famine approach to aid spending never lasts very long. When new threats confront the United States abroad, policymakers invariably turn to the State Department and USAID to confront them. Then, the foreign-aid and diplomacy infrastructure has to be rebuilt, a process that cannot happen overnight. All secretaries of defense since the 9/11 attacks have complained that they were fighting in Afghanistan, Iraq, and Pakistan, and against international terrorist groups around the world, without enough diplomats and aid professionals to stand alongside them. During the Iraq War, in 2004, there was an inverse relationship between the density of USAID projects and casualty rates: the more USAID programs in an area, the fewer U.S. combat-troop casualties there were, according U.S. military research. This is why 121 retired generals and admirals wrote to Congress, which will soon be crafting its own budget, urging the cuts be reversed.

It’s also why powerful Republican senators and a few House committee chairmen announced that the proposed aid cuts were, in the words of Senator Lindsey Graham, “dead on arrival.”