“Just when you think everything that can be said about Obamacare’s constitutionality has been said, along comes another legal brief that makes a new point. The latest was filed by the Arlington-based Institute for Justice, a nonpartisan, libertarian public-interest law firm. The institute points out that the Affordable Care Act’s individual mandate — the requirement to purchase insurance — is not only an unprecedented expansion of federal power. It also undermines several centuries of contract law.”