Donald Trump ran under the slogan of “America First,” which is a noxious expression of nationalism but at least has the virtue of clarity. But his actual foreign policy has been much murkier, in no small part because his global business holdings make it quite plausible that personal financial interests govern his agenda. Trump himself often lends credence to these suspicions by talking about foreign policy as if it were a business enterprise, and not a particularly legal one either.

Trump’s model of foreign policy isn’t the classic realist one of seeking a balance of power or even the imperialist goal of military hegemony but something closer to a pure Mafia protection racket, with weaker states getting American military aid if they keep the coffers full. When he was still a private citizen, Trump outlined his philosophy in a 2014 tweet: “Saudi Arabia should fight their own wars, which they won’t, or pay us an absolute fortune to protect them and their great wealth-$ trillion!” As president, Trump has been able to act out this idea, and the result is, if not trillions in revenue, some sort of shady connection between Saudi money and American foreign policy.

On Saturday, after reports that oil refineries in Saudi Arabia were bombed by missiles from an unknown source, Trump tweeted, “Saudi Arabia oil supply was attacked. There is reason to believe that we know the culprit, are locked and loaded depending on verification, but are waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed!” Subsequently, the Trump administration suggested, without offering convincing evidence, that the attack was sponsored by Iran.

The idea that Saudi Arabia, which is not even a treaty ally of the United States, would set the terms for military retaliation was bizarre. Suddenly “America First” had given way to “Saudi Arabia First.”

Trump elucidated his thinking on Monday when, before starting a meeting with Saudi Crown Prince Mohammed bin Salman, he talked to reporters at the White House. “They’ve been a great ally,” Trump enthused. “Saudi Arabia pays cash. They’ve helped us out from the standpoint of jobs and all of the other things.” On Tuesday, Jonathan Karl of ABC News asked the president if Saudi Arabia shouldn’t be expected to handle its own defense. Trump replied, “The Saudis are going to have a lot of involvement in this if we decide to do something…and that includes payment and they understand that fully.”

Trump’s claim that Saudi Arabia “actually helped us” is ambiguous: Does “us” refer to the United States or to Trump personally? As Matt Yglesias of Vox noted, Saudi officials have been ostentatious patrons of Trump’s businesses: “The manager of Trump’s hotel in New York credited a timely stay by members of the Saudi Crown Prince’s entourage (though not the prince himself) with lifting revenue there by 13 percent in one quarter last year. Lobbying disclosures showed that Saudi lobbyists spent $260,000 at Trump’s hotel in DC back in December 2016 during the transition. Separately, the Kingdom itself spent $190,273 at Trump’s hotel in early 2017.” This is leaving aside Trump’s actual businesses in the Middle East, like the golf resort he owns in Dubai. In truth, Trump’s business dealings are so global and lacking transparency that the extent of his ties to the Saudi royal family is unknowable.

Saudi Arabia is the nexus between Trump’s personal corruption and his flailing, incoherent foreign policy. As The Washington Post points out, Trump’s response to the latest Middle Eastern crisis has been a divided one because he “is caught between a political imperative to confront Iran—pleasing hawkish Republican supporters and allies Israel and Saudi Arabia—and his own political instincts against foreign intervention and toward cutting a deal.” The uncertainty is whether his desire to please Saudi Arabia, Israel, and hawkish Republicans will override his preference, shown in previous foreign policy disputes, to avoid crossing the line between bluster and open conflict.

Trump’s push to make the American army a mercenary force in the pay of the Saudi royal family comes at a time when public opinion in America is becoming more critical of the US/Saudi relationship. Yemen has been engulfed in the world’s largest humanitarian catastrophe thanks to a Saudi-led and American-armed war. This war, like America’s larger interventions in the Middle East, has little popular support.

In April, Congress passed a resolution, which had already cleared the Senate, for the United States to withdraw its support of Saudi Arabia in the Yemen war. Trump vetoed that resolution, a move that was of questionable constitutional legality. After all, if only Congress has the power to declare war, then Trump has no right to veto that resolution. Conor Friedersdorf of The Atlantic contended that Trump could be impeached just for refusing to heed this congressional resolution.

Impeachment, on this or any other ground, seems to be something congressional Democratic leaders have little appetite for. But if impeachment is off the table, investigation is still well within the power and purview of Congress. Given Trump’s repeated statements that Saudi lucre is a good reason for supporting the oil-rich monarchy, Congress has an obligation to ask questions: Is American foreign policy being driven by crassly financial goals? And how much does Trump’s own business dealings with the Saudi royal family shape his policies?

The problem, here as elsewhere in the Trump administration, comes down to congressional oversight. Congressional Republicans continue to serve as Trump’s de facto defense team, while congressional Democrats just don’t have the guts to openly confront the president.