I was looking for a quote on why public education is important to democracy when I ran across this in Quotes on the Importance of Voting.

Now more than ever the people are responsible for the character of their Congress. If that body be ignorant, reckless, and corrupt, it is because the people tolerate ignorance, recklessness, and corruption. — James Garfield, “A Century of Congress” published in Atlantic, July 1877.

Some others:

The man who reads nothing at all is better educated than the man who reads nothing but newspapers. — Thomas Jefferson

Nearly all men can stand adversity, but if you want to test a man’s character, give him power. — Abraham Lincoln

The one I sought:

Whenever the people are well-informed, they can be trusted with their own government.  — Thomas Jefferson