Congress, which forms the Legislative Branch of the Federal government, is responsible for making the laws. The Constitution gives Congress the exclusive power to enact laws, while the executive and judicial branches can only carry out or interpret those laws.
The President has the power to veto any law created by Congress during his or her term. The Supreme Court also has the power to strike down a law if it is deemed unconstitutional. Allowing both of these branches of government to void a law, even though they cannot enact new laws, is part of what keeps the balance of power between the three branches of government in check.