What could the U.S. do to Saudi Arabia for 9/11?

Yesterday, I did a post, "Should 9/11 families be allowed to sue Saudi Arabia?" I received the following question about Obama's options:

@1EMcGon1 Again, what could he do? It's not like they're getting foreign aid he could threaten to withhold, is it?

— Rob Dakin (@Rodak1) September 13, 2016

From the State Department's website:

The United States and Saudi Arabia have a longstanding security relationship and have cooperated closely on this front for nearly 60 years. The U.S. Army Corps of Engineers plays a role in military and civilian construction activities in Saudi Arabia. Three security assistance organizations are funded through the U.S. Foreign Military Sales program: to provide training and support in the use of weapons and other security-related services to the Saudi armed forces; to assist in the modernization of the Saudi Arabian National Guard; and to train and equip a Facility Security Force, part of the Ministry of Interior. The United States has sold Saudi Arabia military aircraft, air defense weaponry, armored vehicles, and other equipment.

On the other hand, there was this story from the Wall Street Journal earlier this month:

China and Saudi Arabia have agreed to a raft of joint development proposals, including construction of oil facilities and housing projects, and shared thinking about security risks during recent meetings, a top Saudi official said Monday. 

“Security was a big thing between us and the Chinese,” Saudi Culture and Information Minister Adel al-Toraifi told The Wall Street Journal on the sidelines of a Group of 20 summit in the eastern city Hangzhou. 

After Obama's Iran deal (the Saudis hate the Iranians), it is clear the Saudis are looking for other options. Withholding security services and weapons sales will only send the Saudis to China.

Even if we got Europe on board with a Saudi boycott, I doubt it would be that effective (Europe tends to be very hit and miss with boycotts). The Saudis could just turn and sell oil to the Chinese.

The key for the U.S. is oil independence, but not only for us. We need it for our European allies. Until then, we have no recourse against the Saudis for 9/11. Even if the families of the 9/11 victims won in court, I doubt we would be able to enforce it in any meaningful way.