Challengers to the health care act emphasize the novelty argument because they have little else on which to rely. Health care, which makes up roughly 18 percent of our gross domestic product, is unquestionably a matter of interstate commerce. The insurance coverage requirement itself regulates a quintessential part of that commercial activity: how consumers pay for medical expenses they will inevitably incur. And past Supreme Court cases interpret the word "commerce" very broadly, holding that it covers even the possession of marijuana for personal use and the growing of wheat for personal consumption.