D--congress and the presidency had taken a hands off approach.
Though presidents from the Progressive Era onward through Eisenhower had the opportunity to address civil rights, they choose not to. Congress also had not made any laws to address the concerns of blacks.
Presidents, especially Democrats, did not want to lose the white southern by promoting civil rights. Congress, containing Jim Crow congressional leaders, were also not willing to advance civil rights legislation. The Supreme Court had the Constitution and a life appointment to do the work of civil rights with no major repercussions to their careers.