Pragmatism is a philosophy where practical consequences and real effects are vital. The mantra is that something is true only if it works or only while it works. If something does not work, then it is not a true form and should be replaced.
The spirit of pragmatism is seen in the founding documents. The Declaration of Independence is a very pragmatic document. The introduction states clearly that the People have the responsibility of overthrowing the government that no longer works for them by altering or abolishing it. This is the central idea of pragmatism.
There are other connections as the US evolved. There are protections against cruel and unusual punishments. This echoes the pragmatic sentiment that practical solutions are the ideal. A cruel punishment would not be practical for a society to employ because it would undermine the authority of the government. Additionally, the Miranda warnings issued by police are a much more recent innovation in law enforcement, but also reflect of the pragmatic manner in which we approach our laws. It is not reasonable or practical to demand cooperation from a citizen if they are not fully aware of their lawful protections. Therefore, it is pragmatic to inform them of their rights before such rights are challenged in court. This practical matter protects not only the citizen, but the government.
The basis for democracy is that people will hold the laws true and right only so long as the government enforces them fairly and equally. When the time comes and laws are no longer seen as true, then the people maintain the freedom to alter those laws to meet a new truth. This is the manner in which the Constitution is altered via the amendment process.