I have been of the opinion for some time (and this may read like heresy to some) that one of the challenges with the US Constitution is that people try to pay it too much respect.
My reasoning is simple. The Constitution is treated by many people, including most of the legal system, as the Supreme Law of the Land. Many Supreme Court rulings turn on whether a law or the interpretation of the law by lower courts is consitutional. If SCOTUS says that all or part of a law is unconstitutional, then the law is immediately presumed to be invalid.
Further evidence (if we needed any) is that when proposed new laws are being discussed, the discussion often immediately jumps past "is this law any good?" to become focussed on "is it constitutional?", the idea being that any law that is unconstitutional is by definition, immediately and irredeemably bad. Witness the discussion about any law that has anything to say about the individual right to own guns. Pressure groups long ago learned to sing the song that all and any perceived restriction on gun ownership is by definition unconstitutional. Whilst I think that some of the song is bloviating bullcrap, and there is an enormous amount of fallacy and some conspiracy theory mixed in, it sure keeps the donations rolling in to pressure groups (cynical? moi?).
All of this would be fine if the Constitution was a watertight legal document covering all modern eventualities. That's where things start to get messy. The Constitution was not written as a law. If it had been, you can be sure that a lot of the language that leads to spirited debate today would have been stripped of ambiguity. The Constitution, as I see it, was really a set of guiding principles, written by a wise collection of individuals, many of whom had lived under what they perceived as tyranny and exploitation, and wanted to make sure that their new country did not fall foul of those same failings.
As a result, the Constitution is, well, kind of slippery. It defined a structure of government designed to ensure that a "tyranny of the majority" could not easily be implemented, it tried to specify and limit the powers of the various branches and levels of government, and it included some great language regarding basic human rights.
The founders were smart enough to define how the Constitution could be changed. However, the core of the Constitution is barely changed from its original version, and the changes that have occurred have consisted of tacking on various Amendments at various times, some of which ended up contradicting each other, often deliberately. There has been no "root and branch" review of the entire Constitution EVER. Unlike (say) the Census, which occurs every 10 years, there is no prescribed interval process for the review of the Constitution. The whole amendment process is ad hoc, and usually lumbers into action when enough people get upset about a specific issue (voting rights, prohibition, term limits etc. etc.). The process as executed in the past has been mostly reactive, not proactive and visionary.
We are (as those of us who are conscious know) in the middle of an election season. I thought I would therefore point readers to this interesting paper written by Bruce Ackerman in which he discusses some of the constitutional issues raised (and mostly ducked) by the 2000 Presidential Election. Ackerman, along with several other scholars, including Sanford Levinson, has long argued that the Constitution cannot be allowed to remain inviolate in the face of changes in the USA and the modern world. I find the last paragraph of Ackerman's paper (which I remember reading back in 2002) to be especially telling:

Suppose I had been reporting on the recent election of Vicente Fox as President of Mexico. I would have described how a mob of Fox’s partisans stopped the vote count in Mexico City, how Fox’s campaign chairman used her authority as chief elections officer to prevent the count from continuing, how Fox’s brother exercised his position as governor to take the Presidential election out of the hands of the voters, how the Supreme Court intervened to crush, without any legal ground, the last hope for a complete count. Would we be celebrating the election of President Fox as the dawn of a new democratic day in Mexico?

UPDATE - This is sort of a shortened version of a longer set of postings that I have been formulating for some time. It is part of the reasoning that follows from a saying that I have (that my friends will soon be tired of hearing), that America has to decide what it wants to be when it grows up. Part of growing up is adjusting your ground rules of life and living. The Constitution is a key part of those ground rules.