The politicians doing the forcing, franklin pierce, stephen douglas, lewis cass, and james buchanan, all either presidents or presidential candidates are supporters of what political position on slavery in the territories?

They were supporters of the idea of popular sovereignty over slavery. This means that they believed that the people of the states should choose whether the state would or would not have slavery as an institution. They didn't want to federally ban slavery in states that wanted to have slaves and that voted on some occasions for such a thing.