Parris knows that the people of Salem are becoming upset over the number of people being convicted of witchcraft and they are especially upset because the people like John Proctor and Rebecca Nurse. Proctor and Nurse are both popular with the people. Parris is telling Danforth that it would be politically bad for those two to be hanged. Parris and Danforth are both very aware of how the people in Andover rebelled against the witch trials there. Danforth, especially, doesn't want that to happen in Salem because he is a man who loves his power and doesn't want to relinquish it. Despite that, Danforth is also a man who does not want to admit he's made a mistake and so he won't grant a pardon to Proctor and Nurse because doing so would be the same as saying he'd been wrong in pursuing them and putting them on trial for witch craft. This is the reason that they vigorously try to get Proctor to confess, so that they have an excuse to avoid hanging him.