<span>I think he probably meant that the Constitution is not to be set in stone and should change to fit the times, which is my the Founding Fathers put in the Amendment process.
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"A constitutional door is left open" refers to the question of whether an action is constitutional or unconstitutional. There is gray area that needs to be discussed.
Absolute monarchy is a system where the monarch, which is chosen based on the dynasty of the current family in power, has complete and total control. In other words, their power is absolute, hence the name.
