No one Congress The state militias The continental army
This term was known as popular sovereignty and resulted in debate over many decades in both State legislatures and the United States congress. It led to tension across the free and slave states, even leading to a event known as Bleeding Kansas in which the residents would determine whether to be free or slave
One problem for the social security system is that there's more and more older people and fewer young people, so if they massively retire, there won't be enough workers to keep the social security system working because not enough taxes will be paid. A possible solution can be an increase the the obligatory retirement age. This would mean that people would work longer before retiring so they would use less social security money.