It is primarily undemocratic in the sense that (as post #4 mentions) it does not provide for direct voter participation, but for representatives who make decisons and then must stand for re-election. I would imagine that direct democracy could run amuck if it were applied too often.
It depends on whether or not you are referring to the original Constitution if you are looking at post 3. The main way in which the Constitution is democratic is that it allows people rights of expression in the Bill of Rights, which is a list of amendments. The Constitution can be amended through a democratic process because the elected representatives of the people are the ones amending it.
There are other important ways in which the Constitution is not democratic. For example:
- It does not give the vote to women.
- It allows slavery.
- It has the president being elected by an Electoral College, not by the people.
- It has (originally) Senators being elected by state legislatures, not by the people.
In these ways, you can say it is undemocratic.
The Constitution certainly created and helps to uphold a democratic nation. It outlines and sets in place a particular democratic government and set of laws. It could be argued, however, that the creation of this document was notably undemocratic. The men who wrote the Constitution were not necessarily elected. Certainly they were great leaders, but there was no formal election process in place to select them to write this document. The Constitution was written behind closed doors and signed by the authors. It was not voted on in the same way that laws and bills are voted on today. The people of the newly forming American nation didn't have the same ability to offer input and make a selection that we enjoy today.