For the White House, arms sales appear to be the ultimate tool of foreign policy: a flexible way to support allies and partners, who face internal challenges such as terrorism and insurgency, as well as external threats from dangerous neighbors, without putting American boots on the ground. And it’s a tool for exerting leverage over the recipients of American weapons that offers an economic boon to U.S. companies.

Since the terror attacks of Sept. 11, 2001, arms sales and transfers have been a central tactic in the U.S. war on terror. From 2002 through 2019, the United States sold about $215 billion worth of weapons to 169 countries, as calculated by the NGO Security Assistance Monitor, including many where the risks should have been obvious. This list includes autocratic nations such as Saudi Arabia and Nigeria that have used American weapons to kill civilians at home and abroad, nations such as Colombia and Paraguay while they were gripped by civil conflict, and places such as the United Arab Emirates and Uganda that host well‐​established black markets for American weapons.

In these places, U.S. arms have not brought stability, much less peace. Instead, in many cases they have led to increased homicide rates and fed state‐​sponsored violence, and may have exacerbated rather than ameliorated terrorism and civil conflicts.The U.S., for instance, has delivered millions of dollars in weapons to Nigeria since Trump took office and the country is notorious for losing these weapons to Boko Haram— the exact group the weapons are being sold to fight.

Despite the steadily accumulating evidence that arms sales to corrupt and troubled nations have had negative consequences, the American arms sales portfolio has only become more dangerous since the George W. Bush administration.

At the Cato Institute, we developed an Arms Sales Risk Index to assess the likelihood of negative consequences of sales such as weapons being stolen, used against civilians or deepening a conflict on a 0‐​to‐​100 scale. The risk score of the average American weapons customer has risen from 39 under President George W. Bush to 41 under President Barack Obama to 48 during the first three years of the Trump administration. To put those figures in perspective, the average nation’s risk score in 2019 was 39, while NATO countries average just 17.

Sadly, it doesn’t look like Trump worries much about these risks. Though his predecessors all sold plenty of weapons, Trump’s revision of the Conventional Arms Transfer Policy, the White House’s primary policy for weapons exports, makes clear his unprecedented emphasis on the economic benefits of arms sales.

When Congress raised the prospect of cutting off weapons sales to Saudi Arabia in the wake of the murder of the journalist Jamal Khashoggi, for example, Trump responded that, “I don’t want to lose all of that investment being made into our country. I don’t want to lose a million jobs, I don’t want to lose$110 billion in terms of investment.”

Critics complain that the travel ban was just a thinly disguised anti‐​Muslim move given the populations from the original seven countries that were barred — Trump did not, for example, ban travel from Thailand or the Philippines, states without Muslim majorities where substantial terrorist activities take place.

Though there may be some truth to this argument, the average risk index score of Trump’s proposed group of travel ban nations is a staggering 69 out of 100. These countries suffer from much higher than average rates of terrorism, human rights abuses and political violence; are far more fragile than most; and are much likelier to be engaged in both internal and external conflicts. Caution in managing relations with these nations is clearly in order.

What does not make sense, however, is prohibiting people from these countries from traveling to the U.S. while continuing to sell their governments the very weapons that may make them even more dangerous.