Answer: by comparing the goals outlined in the Preamble to what the government has achieved.
Explanation: The Preamble is the opening to the US Constitution which explains why the government was created as a republic. The main purposes of the Preamble are, to serve as an introduction for the Constitution; to outline the goals of a united government as originally designed by the Framers; to explain the purpose of the Constitution and to establish that power of the government comes from the people and not from those in power.
The goals of a united government as outlined by the framers were:
1. To form a more perfect Union
2. To establish Justice
3. To ensure domestic tranquility
4. To provide for the common defence
5. To promote the general Welfare
6. To secure the Blessings of Liberty to ourselves and to our Posterity.
These goals can be used to measure if the government has been living up to its expectations.