There are a few legal arguments the US can and will use against this.Violation of sovereignty and force prohibition: The U.S. military action on Venezuelan territory and abduction of a sitting head of state is a significant violation of Article 2(4) of the UN Charter, which prohibits the use or threat of force against the territorial integrity or political independence of any state without UN Security Council authorization or self-defense justification
1) They did so with the consent of Venezuela's lawful administration. As Maduro is widely accepted to have stolen the election, the permission of those who really did is enough
2) Not a "use of force". The US can (and will) argue that this was not a use of force within the scope of the article. It was not a military operation, it was a law enforcement operation, etc.
3) The philosophical argument. If a law doesn't carry any punishment or any mechanism with which to cause or create a punishment, does it even count as a law? The US has a veto in the security council, so it's impossible for the US to be found in breach and have any action taken. So if it can't be found to have breached the law, it must be lawful.