Suppose that the State of Maryland passes a statute (laws passed by legislatures) that severely restricts electric cars in the state. A group of automobile manufacturers files a suit against the State of Maryland to prevent enforcement of the law. The automakers claim that a federal law already allows electric cars to be made statewide. According to the automobile manufacturers, it is unfair to allow Maryland to impose different regulations than those set by the federal law. Using the information presented in the chapter, answer the following questions. What is the primary source of the law that is at issue here?