The previous post is quite accurate in the assertions made. I would contend that the fulfillment or striving to meet the needs and dreams od a diverse American body politic has matched up quite well with the goal of the Constitution, "in order to form a more perfect union." The nation has been perfectly imperfect in its ability to understand the dreams of those who had been on the outside looking inwards. Yet, it never fled from its fundamental responsibility of seeking to meet the needs of these individuals. Whether it was "the dream" for African- Americans, the demands of "equality now" for women, or the hopes for Mexican- Americans, Asian- Americans, groups that have emigrated to the United States, and the dreams of equality for gay and lesbian and transgendered individuals, there has been a process of seeking to hear and validate such voices and experiences. No one would ever suggest that these groups have been perfectly assimilated into the American discourse. Yet, there has been improvement. There has been progress, and, to quote the President, "This is where we have to start in order to form a more perfect union." The idea of democracy being an unfinished experiment has been demonstrated quite well in the post war American political discourse.
I would say that American democratic politics and values have served diverse people imperfectly. This is sort of like the story of our country in general -- these people have not been served perfectly, but things are tending to improve over time.
Clearly, there are many "minority" groups who continue to have grievances even today. People of color are generally poorer than whites. The criminal justice system seems to be more punitive to them. Gay people lack what they consider to be basic rights. Even women continue to have what some consider to be problems in securing equality.
At the same time, however, things are so much better than they were at the end of WWII. The democratic process has given rights to minorities and to women that were unthinkable in 1945. This shows me, at least, that things are generally improving.