We don’t know the full story with the Saudis and the Trump family. But we know a lot. We know that Trump benefited from big flows of Saudi money before he became President. We know because he told us. We know he was twice bailed out from possible bankruptcy by Saudi princes. We know his son-in-law and top advisor Jared Kushner has built a close relationship with the Saudi Crown Prince. We know Kushner has used that relationship to at least solicit private funds from Saudi Arabia and the United Arab Emirates, which runs in regional foreign policy lock step with the Saudis. We know finally that both countries were working to support and move money to the Trump campaign during the 2016 election.

My point here is not to say that we know the particular relationship between the Trumps and the Saudis. For these purposes, I don’t think we need to. My point is that whenever there are high stakes decisions to be made in the US-Saudi relationship, there’s really no way to know what is done for policy reasons versus the personal and/or financial interests of President Trump and his family. The same applies to Russia. The same applies to a number of other Gulf states which are either allies or enemies of the Saudis. Even with Turkey in this case, it’s hard to know just what President Erdogan is doing vis a vis the United States because we don’t know what he knows about the relationship between the Trumps and the Saudis.

The possibility, really the probability, of corruption is the most obvious and immediate problem with this situation. But everything also simply becomes more opaque. Foreign relations are by their nature secretive. But in usually we can have a relative confidence that the President and his or her top advisors have a general view of foreign policy, an ideological position or way of approaching foreign relations, and they are using that map to make decisions which they believe are in the best interests of the United States.
...
Our suspicions should be heightened by the fact that President Trump seems to gravitate toward world leaders who run autocratic regimes and run oligarch-type states. If you develop a close relationship with Angela Merkel, she has no real way to steer millions or billions of dollars to your private company. It just doesn’t work that way. She’s not the state. Sure, corruption is always possible. But she’s just a temporary occupant of the leadership of her country. The same applies to most reasonably non-corrupt democracies. The Gulf States are very different, as are the post-Soviet states. China is different but it has significant similarities. The fact that Trump is an oligarch-type figure, maintains an opaque private company while serving as President and is notoriously corrupt fundamentally changes US foreign policy and what we’re able to know about it. Because we can’t know what is happening our ability to affect it through democratic means is diminished.

https://talkingpointsmemo.com/edblog/welcome-to-the-era-of-oligarch-foreign-policy