I know that all of you knew this, but here's the long and boring legal answer. I hear this question - where in the constitution does it say that you are entitled to health care? The answer I usually hear is in the preamble. There's actually an even better answer.
First, it's a trick question - yes, it's true that the constitution does not say anything about health care, specifically, nor does it say that the government can build highways and bridges. However US Const. Art. I, Section 8 states:
"The Congress shall have power to lay and collect taxes, duties, imposts and excises, to pay the debts and provide for the common defense and general welfare of the United States."
That means that Congress can tax and spend for whatever it chooses, including health care, highways, and bridges, unless another part of the constitution forbids it (for example, the 1st amendment bars Congress from spending money for religious activities). So the question really should be, where does the constitution forbid Congress from passing health care reform.