Congress always keeps a watchful eye on the President. Same for the opposite too, the President keeps an eye on congress. Congress checks the President by if there's a 2/3 majority vote to override his veto.
The Dred Scott decision, or lawsuit as you put it, was a case where it was stated by the court that people of African descent could not be American citizens and had no standing in court. They, whether free or not, had no power to regulate slavery in the United States. His rights have been violated for many reasons. He was accused of standing in court for just being black. It was very unconstitutional and found by many historians as one of the worst Supreme Court decisions ever made.
I believe this one would be All of the above
