Separation of powers under the United States Constitution
Congress has the sole power to legislate for the United States. Under the nondelegation doctrine, Congress may not delegate its lawmaking responsibilities to any other agency. In this vein, the Supreme Court held in the 1998 case Clinton v. City of New York that Congress could not delegate a "line-item veto" to the President, by powers vested in the government by the Constitution.

Q: What is the only branch of U.S. government imbued with lawmaking abilities?
Congress