The powers in the constitution granted the government are not explicit in terms of the commerce clause and the necessary and proper clause. Both clauses are purposely vague to allow for the government to bring about legislation they consider necessary and proper to provide regulation of commerce unless that legislation is explicitly prohibited in the constitution. Since there is no clause that prohibits the Congress and the POTUS from passing this mandate, it therefore falls under the powers of that elected body to enact legislation as it sees fit. The people then have the power to toss them out and start again if they so desire. The argument goes to regulating so-called inactive economic activity. Since we have a law called the EMPTALA act which allows for free emergency care to be provided under certain circumstances at certain medical facilities for anyone regardless of ability to pay, we are in affect providing free emergency care to anyone who steps onto the soil of the USA. By forcing the rest of us to subsidize this free care because we decided through our elected officials to help those in need regardless of status, we are allowing for inactivity on the part of uninsured citizens to be part of the national cost of medical care. Therefore, if the costs of this inactivity is regulated, that is, it is mandated across the nation that everyone can get care, then the Congress can take this one step further and say that these people must pay for it or be subsidized directly in order to get this care via a different means.