Final answer:
Jefferson believed that when a government fails to protect citizens' rights or becomes a threat to them, it is their right and duty to overthrow that government and establish one that secures their safety and happiness, based on the social contract theory.
Step-by-step explanation:
According to Thomas Jefferson, people have the right and responsibility to overthrow their government when it becomes destructive to the inalienable rights of life, liberty, and the pursuit of happiness. Jefferson, drawing on the philosophy of John Locke and the principles of the social contract theory, argued in the Declaration of Independence that a government's legitimacy stems from its ability to protect these rights, and it governs only with the consent of the governed.
When a government fails to protect these rights, or worse, becomes a threat to them, it is not only the right but also the duty of the people to alter or abolish it. This provision meant the creation of a new government that would better safeguard their safety and happiness. The principles highlighted by Jefferson underscored the reason for the American colonies' decision to declare independence from Britain and established a foundational concept that would influence the development of the United States government and other democracies around the world.