Final answer:
The glue that holds a republic together is the virtue of its citizens, which is crucial for maintaining a government 'of the people, by the people'. Civic virtue and successful maintenance are essential for a republic to survive, as mandated by the U.S. Constitution and evidenced during the Federalist Era.
Step-by-step explanation:
The glue that holds together a republic is essentially the virtue of its citizens, as outlined by political theory. It is the public virtue that allows the republic to survive and maintain its integrity; without it, the republic may fall. In the context of the United States, from its inception, there has been an emphasis on the need for civic virtue — the idea that people must put the common good above their personal interests. This is a fundamental principle within a republican form of government, as the Founding Fathers believed, and is essential for sustaining a government 'of the people, by the people.'
Furthermore, the successful maintenance of a republic against internal challenges is crucial. This is evidenced by the debates and decisions during the Federalist Era and the expectation set in the United States Constitution, Article IV, Section 4, which mandates a republican form of government for the states. By fostering a society where virtuous citizens elect representatives to govern, the republic maintains its democratic principles while guarding against potential corruption that could threaten its stability.