Nancy's answer is because she does not know and does not care. Not many in Congress will be bringing a covered dish to the MENSA meeting.
Commerce is a possibility, but I have heard some over the years cite "promote the general welfare" to justify a myriad of interventions. I suppose the Pres. could invoke some type of emergency power.
I'm surprised someone has not challenged the notion that there is any constitutional authority for a lot of the most recent actions; and I include Bush's economic actions.
I just heard a very interesting question and thought this would be a good place to raise it: Where does the Federal Government find the Constitutional authority to require individuals to buy health insurance? I would imagine the answer lies somewhere in the commerce clause but I'm interested to hear everyone else's thoughts.
P.S. Nancy Pelosi's answer to that question: "Are you serious?"