At The American Conservative, Daniel Larison reminds readers that Saudi Arabia is not an ally of the United States in any sense of the word. He writes (abridged):
The U.S. is not obliged to come to Saudi Arabia’s defense.
No matter who was responsible for the attack on their oil installation, the U.S. has no business responding with military action. Saudi Arabia is not an ally in any sense of the word. We have no mutual defense treaty with them, and we are not required to come to their aid when they are attacked.
Even if the U.S. were obliged to come to the Saudis’ aid, the president cannot initiate hostilities on the say-so of a foreign government. An attack on Saudi Arabia is absolutely not considered an attack on the U.S., and unless Congress authorizes military action the president cannot legally order a military strike against anyone under these circumstances.
If the president ordered military action against anyone in response to this attack, he would be acting illegally and violating the Constitution.
Congress must make it clear that he does not have their support in this matter, and any military action that he orders will be unauthorized and unconstitutional.
It also might be worth remembering that as recently as 2014 Saudi Arabia attempted to kill off an entire U.S. industry (shale oil) by dumping as much crude on the world oil market as it could. These are the people who would now have America fight a war for the same oil fields they used to do it.
Read more from Larison here.