The writers of the U.S. Constitution quoted Montesquieu more than any other source except the Bible.
Montesquieu wrote in The Spirit of the Laws, Book 24:
“In a Popular state, one spring more is necessary, namely, Virtue …
The politic Greeks, who lived under a Popular government, knew no other support than Virtue …
When Virtue is banished, ambition invades the minds of those who are disposed to receive it, and avarice possesses the whole community …
When, in a Popular government, there is a suspension of the laws, as this can proceed only from the corruption of the republic, the state is certainly undone.”