That is what set Martin Luther King, Jr. apart from others.
A good source for this election is the book Render Unto Caesar. It has the subtitle of Serving the Nation by Living Our Catholic Beliefs in Political Life.
This book is written by talented writer by the name of Charles J. Chaput, O.F.M. Cap., who also just happends to be the Archbishop of Denver in the Roman Catholic Church.
In Chapter 8 of this book, titled Conscience and Cowardice, author Chaput spends the last part of the chapter (a few pages) on Letter from a Birmingham Jail, written by Dr. Martin Luther King, Jr.
This chapter spans pages 138-157. The part on MLK Jr is only from pages 154-157. The following is the last two paragraphs of this chapter of Archbishop Chaput's book:
[Dr. Martin Luther] King [Jr.] was deeply troubled that the world so readily dismissed the Christian church, Christ's community of disciples, "as an irrelevant social club with no meaning for the 20th century." He lamented, "In deep disappointment I ahve wept over the laxity of the Church." King had little use for lax Christians. Neither should we -- especially if the lax Christians are us. We have no excuses. We have too many models of courage to guide us.
Dr. [Martin Luther King, Jr.] and his followers were willing to go to jail for conscience' sake. His "Letter" is an example of using language in the service of truth; of the power of words to compel action consistent with God's higher law; of a healthy and articulate Christian conscience. His "Letter" also reminds us that too many of us are willing to live quite comfortably as cowards. King wrote that "human progress never rolls in on the whells of inevitability; it coms through the tireless efforts of men willing to be co-workers with God, and without this hard work, time itself becomes an ally of the forces of social stagnation."
It should be noted that I am quoting from a public library copy of this book. I live in a Catholic city that believes in putting a book like it in it. This is Lafayette, Louisiana, and I am proud to say that. I had no pride living in New York City, NY -- the abortion capital of the United States -- in my opinion.
Here is that footnote, complete with a PDF link to the letter as well as the link by the Alabama Clergymen that sparked it:
16. Martin Luther King Jr., "Letter from Birmingham Jail," available from stanford.edu/group/King/frequentdocs/birmingham.pdf; for the "Statement of Alabama Clergymen" that sparked it, see stanford.edu/group/King/frequentdocs/clergy.pdf.
[Footnotes for Chapter 8: Conscience and Cowardice]
Note that there are embedded links to the PDF's (which the book cannot have since it is an old fashioned book -- you cannot click on books -- though you may be able to scan them...)