“No part of the government has a legal duty to protect the citizens. This is black-letter law.”
Where did you read that?
The purpose of our Federal Government, as found in the Preamble of the Constitution, is to “establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our posterity.”
If that doesn’t confer a legal responsibility on government to protect the citizens then we may as well throw the Constitution into the garbage can and declare The people of the United States of America as slaves who live at their master’s will.
I’ve read it in numberous places. See http://www.freerepublic.com/focus/news/1976377/posts for a short collection.