Saudia Arabia has control over a huge amount of oil. That, in itself, could be a huge threat to the oil-dependent United States. Saudia Arabia is also an extremely rich country with many different resources at its disposal. Could a cell of terrorists be hidden, trained, and financially supported in Saudia Arabia? Almost certainly.
Saudi Arabia has been an uneasy ally of the United States for quite some time. This relationship should be treated with immense caution because Saudi Arabia continues to have ties to places in the Middle East where terrorist cells have been discovered. This means that at any time Saudi Arabia could become an immense threat to the safety of Americans.
Never forget what happened on 9/11 and after. When all planes were grounded, the only one allowed to fly was a Saudi one, full of members of Bin Laden family and Embassy employees. For years many government,especially Iran,insisted on the terrorist essence of Saudi rulers and their economical,political and logistic support of extremist groups like Al-Qaeda , ISIS ,Al-Nusra ...
Saudia Arabia is a mostly peaceful country and is not a threat to the U.S. In fact, if we were to combine forces with Saudia Arabia they could be a powerful ally. They have a wide range of resources and influence, and can help the US achieve it's goals as a nation.