Rawls' ideas are frequently cited as the justification for the institutions we see in our United States government, such as programs to address poverty. To achieve something like "fair equality of opportunity", we have to do something to address factors that could affect one's ability to get an education and compete for the best jobs. And if we are to say that our social and economic inequalities are arranged so they are "to the greatest benefit of the least advantaged," then it seems as though there must be some limit to the amount of social and economic inequalities that exist, and that those inequalities must be part of a narrative tied to the benefit of the least advantaged. In America, we call this narrative the American Dream. "Our country has a reputation for being a place where individuals can change their economic and social circumstances in a predictable way based on individual effort and merit." 
But the fact that rational actors would agree to Rawls' two principles, which he calls "Justice as Fairness", does not establish any necessary connection to our United States Constitution unless the principles themselves are accepted as having the same meaning as specific elements of the Constitution (including Amendments). There is significant disagreement on this point. However, we can describe much of the controversy in our American political system as conflict between competing ideas of what the government can or should do to achieve Rawls' second principle without violating his first principle.
In Anarchy, State and Utopia (1974), Robert Nozick articulated an elegant libertarian rebuttal to Rawls. Nozick's argument for the minimal state made reference to a state of nature with an assumed natural law that gives us individual rights similar to what John Locke envisioned. Nozick asserts we could expect enforcement, protection, and arbitration mechanisms to evolve into a limited government from such a state of nature. He denies there is any legitimate role for a government to address anything beyond what he labels as the functions of a "night watchman"--protecting citizens from violence, theft and fraud. According to Nozick, there is no role for the government to redress economic inequality. On this view, anything more than the minimal state we could expect to evolve naturally is a violation of the natural rights of some citizens.
The contrast between Nozick and Rawls theories of justified governmental powers comes down to different views of how to protect property rights. Rawls essentially asserts that the most fair way to define the rules of society is to settle on the rules to which we would agree if we had no knowledge of our economic status. Nozick says that, since we do have knowledge of our economic status, the only legitimate powers of government are those we would agree to in the state of nature, without regard to our economic status. This contrast is the same contrast we observed between the actual language of Magna Carta, which explicitly protected only the top 24 percent of the population, and the more egalitarian myths about Magna Carta, which extended those protections to all subjects of the king.
One more social scientist--Thomas Sowell--offers a synthesis of sorts between the competing ways of generating rights and responsibilities. We'll take up Sowell's argument from A Conflict of Visions in our next blog.
 Rawls, John, A Theory of Justice, Harvard University Press, Cambridge, MA 1971, pp. 302-303
 Tryon, Stephen, Accountability Citizenship, XLibris, 2013, p. 71.