Why was franklin roosevelt’s attempt to stack the supreme court an abuse of power? because the president should not associate with the justices because the executive branch cannot dictate legislation by manipulation because the president cannot nominate more than one justice in his term because the supreme court is required to have only nine justices

The best answer is 
because the president should not associate with the justices

The president should not wield his power to nominate justices as a tool for political power. The President should respect the independence of the judicial branch. To fill the Supreme Court with political allies would essentially give the president control over both the Executive and judicial branch. Indirectly, the power of his veto and the Supreme Court's power of judicial review would also give him great influence over the legislative branch as well.