Something Trump said in a recent interview perfectly captures his misguided, mercenary understanding of international relationships:

In an interview with The Wall Street Journal on Tuesday, Mr. Trump said he wanted to believe Prince Mohammed’s denial of any foreknowledge of Mr. Khashoggi’s death.

“They’ve been a very good ally,” Mr. Trump said. “They’ve been a tremendous investor in our military equipment and other things. They buy tremendous amounts of things from our country [bold mine-DL].…So I certainly want to believe him.”

Saudi Arabia isn’t really an ally at all, and it is all but impossible to grant that they have been a “very good” one in recent years. Saudi Arabia’s destabilizing and reckless behavior doesn’t concern Trump, and he isn’t judging them by their international behavior in any case. Trump’s attitude towards an “allied” government depends almost entirely on whether or not he thinks they pay us enough. If he believes that an ally is ripping the U.S. off in some way, he is extremely critical of that government and sometimes even becomes hostile to their leaders as a result. On the other hand, if he thinks that they “buy tremendous amounts of things,” he doesn’t want to say a bad word about them and doesn’t want to do anything to upset the relationship. This is consistent with his protection racket/tribute view of relations with other countries, and it shows that advancing U.S. interests never really factors into his thinking. That is why he is so protective of the (exaggerated) arms sales to the Saudis, and it’s why he has no problem subordinating U.S. interests to those of regional clients.

The Trump administration treats arms sales to client governments almost as ends in themselves, and they seem to think that the continuation of those sales justifies continued support for whatever disastrous policies the clients implement. As Hanna and Cambanis explain in their article on Yemen, this gets the relationship between U.S. interests and arms sales backwards:

The problem of weapons sales transcends the Yemen War and has contaminated a growing swathe of U.S. policy. Weapons sales have acquired a pernicious logic of their own, as if funding the U.S. weapons industry were a jobs creation program and national security policy simply a means to promote domestic economic growth. U.S. weapons sales can be a major driver of conflict and have routinely complicated foreign policy in regions where the imperative to maintain market shares conflicts with core U.S. interests. In specific cases like the Yemen War, where weapons sales run so thoroughly against U.S. policy goals, they should end conclusively.

To date, the United States has been almost entirely unwilling to give up any weapons contract, no matter how noxious, because of the adverse impact to the U.S. economy. This type of path dependency is counterproductive. The United States must be willing to forego profitable contracts that harm our interests or bind us to ineffective allies or specific misguided policies.

In Trump’s view, a government that buys lots of weapons from the U.S. is a “very good ally” simply because it is a large purchaser of U.S.-made weapons regardless of what it does with those weapons. That helps explain why Trump is so adamantly opposed to cutting off those sales, since he sees the arms sales as the defining feature of the relationship and the thing that separates the “good allies” from the rest. He can’t imagine why the U.S. should forego arms sales profits for the sake of other interests, much less for the sake of principles, and so he sees no reason not to keep arming a government guilty of numerous war crimes.