Answer:
creating a law ex post facto
Explanation:
A law ex post entails such a law which punishes people for a crime that was not a crime when it was committed. Congress cannot pass these laws.
A law ex post is is that law which refers to peoples actions or crimes, which they have carried out or committed before before the law was made. Such law can be uses to punish those individual's but can never be passed by Congress. Hence, it is a forbidden factor in the constitution.
