What are some similarities between the Declaration of Independence and the U.S. Constitution?

[George S]

They both deny absolute authority for government.

I'm not sure if he's trying to twist them into the kind of "social contract" socialists commonly promote. That was being relegated during the time those two documents were created. They reinforced freedom from the parent-child obligations of government toward citizens. Bourgeois true liberalism (see below) was rising to replace the conservative aristocracy's "social contract" obligations with peasants and the rising proletariat of industrializing Europe.

The two documents stemmed from that breaking of social contracts between the three classes. They tacitly declared no class distinctions, and even outlawed official aristocracy. The concept of social contract under those documents was an implied obligation of government to not interfere with, or exploit, citizen's efforts more than really necessary. Citizens are obligated to support that government so long as it wasn't too repressive or oppressive, and correct or remove it when it is.

That isn't really the kind of "social contract" Rousseau imagined between French aristocracy, peasants, and proletariat, nor is it the kind promoted by socialists since. I'm not sure what your teacher is implying, but it is common today for socialists to twist whatever is convenient to twist in promoting their philosophies. They often call themselves, and today are too often falsely called, "liberal" when they are far from that.

True liberalism advocates: individual freedom, weak government, and free markets. Conservatism advocates: moral responsibility, strong government, and protected markets. Progressives advocate: social concern, omniscient government, and controlled markets. Socialism advocates: social responsibility, omnipresent government, and collective markets.