The Constitution provides the fundamental architecture of the US Government. As such, it lies at the very center of the country's political traditions. However, at the same time, US political culture and society has changed dramatically since the Constitution was first written. Technology has advanced since the late eighteenth century, with the advent of industrialization and, more recently, the digital age. Demographics have been transformed as well, from a primarily rural society to a far more urbanized one, with populations more densely concentrated in urban and suburban areas.
The result of these changes has seen a dramatic increase in centralized power, particularly within the Executive Branch. The Federal Government (and the Presidency) is far more powerful than it was in the early Republic. At the same time, moral norms have been transformed as well. Even so, however, the core understanding of US democracy as a government for the people, founded in the understanding and respect for peoples' rights, has remained a continuous thread across this long scope of US political history.
The Constitution is key in navigating these various political disputes, both concerning the protection or limiting of political rights as well as in the government's exercise of its political power. The Constitution is the political document that gives the US government its very legitimacy, and in these political disputes, the Constitution itself tends to be the final arbiter.
However, at the same time, it is worth noting that there are different traditions toward reading the Constitution and applying its principles to contemporary issues. (Thus, in these kinds of political disputes, both sides within a dispute would, in many cases, invoke the Constitution as supporting its position. This dates back to the very earliest history of the United States, where you can observe both Alexander Hamilton and Thomas Jefferson invoking the Constitution to argue for and against the creation of a National Bank).
In almost all cases, however, the Constitution itself remains of critical importance.