Final answer:
Jefferson believed states could nullify federal laws they found unconstitutional. This concept was expressed in the Kentucky and Virginia Resolutions.
Step-by-step explanation:
Thomas Jefferson believed that if a state did not approve a federal law, it had the right to engage in nullification, which included interposition or nullification by blocking federal laws they deem unconstitutional.
Jefferson and James Madison expressed this idea in the Kentucky and Virginia Resolutions as a response to the Alien and Sedition Acts of 1798. These resolutions asserted that states could judge the constitutionality of federal laws and declare them to have 'no force' within their borders.