The Constitution also mentions the promotion of interstate commerce. Do you see much commerce going on right now?
I am more libertarian than all but a tiny handful of posters on this site, but if there's really no better answer to the fragility of our power grid than, "well, they're private companies; it's between them and their customers", then Bush would do well to nationalize the entire system today. (That's a "modest proposal", for those of you following along at home; of course there's a better answer.)
Market forces are preferrable to command economics, but in our economy the power grid underlies the market. Short circuit the power grid and you disconnect many of the forces you were counting on. Of course the government has a responsibility to get the power back on ASAP, if for no other reason than that the government can't fulfull its other responsibilities without it. If intervention can help facilitate that, then that's what should happen.