Separation of powers is the constitutional design that gives different jobs to different branches. Congress writes laws and controls federal spending. The President enforces laws, leads the executive branch, and conducts many foreign affairs duties. Federal courts decide cases and interpret law. The goal is not speed; it is guarded power. Each branch has authority the others do not hold, and each can be checked by the others. This is why a law may be passed by Congress, signed or vetoed by the President, interpreted by courts, and carried out by agencies.