<span> 1. The constitution - the legislative branch cannot enact laws that violate the constitution. this limit is kinda limited in that the legislative branch could vote to change the constitution, but it would be extremely difficult and would also need ratification by 2/3 of the states.
2. the president- congress can pass laws, but they are not official laws until the president signs them. the president can refuse to sign a law the legislative branch has passed or veto them. with a super majoiity the legislative branch can override a veto though.
3. the people - the people vote for who is in the legislative branch. if we dont like what they do we can vote in new guys.</span>
I don’t know this give me some details
The clause is really a state's rights clause. A state may not pass a law that makes something illegal that was legal before the law was passed. In other words if a state suddenly passed a law that said it is no longer legal to park your car in front of any government building, but it was legal to do so yesterday, the police cannot come to your door and issue a ticket for parking in front of a government building because you did it yesterday.
The constitution actually uses the phrase ex post facto law in Article 1 Section 10 Clause 1.
