What key principle underlay the judicial reasoning in both McDonald v. Chicago and U.S. v. Lopez?

The judicial reasoning in both McDonald v. Chicago and U.S. v. Lopez is fundamentally underpinned by the principle of limits on government power. In McDonald v. Chicago, the Supreme Court addressed the issue of whether the Second Amendment right to keep and bear arms is applicable to the states through the Fourteenth Amendment's Due Process Clause. The Court's decision emphasized that states cannot infringe upon this individual right, thereby reinforcing the limits of government authority over personal liberties.

Similarly, in U.S. v. Lopez, the Court examined whether Congress had the authority to regulate gun possession in school zones under the Commerce Clause. The ruling determined that such regulation overstepped federal power, reiterating the boundaries of governmental reach and upholding states' rights and individual freedoms. Both cases reflect a legal commitment to constraining government power in order to protect individual rights, establishing a robust interpretation of personal liberties within the framework of the Constitution.