I think the central issue is that the US is highly susceptible to special interest lobbying. Yes, I believe you can take that bet to the bank. We see it every day in Washington and across most segments of the system (from security to various industries to domestic and foreign policy).

There's no conflict between that and the routinely chaotic and irrational foreign policy of the US. They can both exist side by side. Some of the foreign policy irrationality is in fact caused by domestic lobbying, we've seen that throughout post-agrarian US history where the US Government intervenes in foreign affairs on behalf of powerful domestic commercial interests. A further cause of that foreign policy irrationality is at least in part due to administration changes over time, with which agendas change. Adminstrations change, domestic lobbying continues. If you need to think long-term, and you change plans every four to eight years or similar, you're inevitably going to get chaos and wild unintended outcomes. Consider all the plan changes from Bush to Obama to Trump in Afghanistan. I'm not arguing that their goal is necessarily chaos, rather, it's the inevitable product of the approach.

I'm not arguing that acting on behalf of domestic oil interests that might want to see Saudi's output hampered, is rational. Indeed, that might very well be another ideal example of irrational, dangerous behavior that could cause more instability. When trillions of dollars are at stake, one thing you can assume is lobbying toward the dollars will be involved.

I don't believe there's any meaningful US Government loyalty to Saudi Arabia beyond a matter of oil convenience. Trillions of dollars at stake over time as it pertains to domestic oil production, is worth a lot more than the arms purchases from Saudi Arabia. As the US oil production figures continue to rise year after year, the powerful interests represented in that will want higher prices. Their influence increases as the production does (and Saudi's influence declines).

Saudi is set to become primarily a competitor of one of the largest, most important industries in the US. Rather than a relationship of shared security (they get system security, we get oil security), it'll become a relationship of growing animosity / tension, which we're already seeing the early beginnings of (Congress being willing to invoke its war powers to try to force an end to the US support of Saudi re Yemen; and their increasing willingness to criticize Saudi generally).

When it comes to the rest, why should the US care about Syria strategically? The US should have never been over there in the first place. The only people that want us there are the war hawks.

The next administration after Trump will yield more new chaos, as plans and agendas change. It's the inevitable consequence to being perpetually in a position of war and meddling in foreign nations. You're always there as a nation and the people controlling the meddling come and go, with each change lighting new unintended fires. I'd argue that any involvement choices made in the Middle East other than to entirely pull out of the region, are by default irrational. There's no winning or rational direction if you're doing what we're doing, only fires to constantly be put out while you're in the muck of it.