Martin Luther King , Jr.

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In this Feb. 5, 2015 photo, a group gathers at Congregation Mishkan Israel in Hamden, Conn., to remember when Dr. Martin Luther King, Jr., visited the temple to preach on Oct. 20, 1961. King is shown second from right in the 1961 photo with leaders of the temple at that time. (AP Photo/New Haven Register, Peter Hvizdak)

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U.S. Sen. Rand Paul appeared in a black and white TV spot for MTV on Monday, calling for a unified America in honor of Martin Luther King, Jr. (MTV)

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"Protest courageously, and yet with dignity and Christian love," urged Martin Luther King, Jr. in his Montgomery bus boycott memoir "Stride Toward Freedom." Above: A dedicated copy of the book. (AP Photo/Rogelio V. Solis)

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Charles Ogletree, the Harvard Law professor who mentored President Obama and the first lady during their time in Cambridge, has compared the Aug. 9 shooting of Michael Brown to the 1968 assassination of Dr. Martin Luther King, Jr. (YouTube/National Review)

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Firemen and National Guardsmen were called out to quell rioting that broke out in Washington following the news of the assassination of Dr. Martin Luther King, Jr., April 6, 1968. (AP Photo)

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Firemen and National Guardsmen were called out to quell rioting that broke out in Washington following the news of the assassination of Dr. Martin Luther King, Jr., April 6, 1968. (AP Photo)

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National Guardsmen were called out to quell rioting that broke out in Washington following the news of the assassination of Dr. Martin Luther King, Jr., April 6, 1968. (AP Photo)

AP080718016175

Firemen and National Guardsmen were called out to quell rioting that broke out in Washington following the news of the assassination of Dr. Martin Luther King, Jr., April 6, 1968. (AP Photo)

AP080718016167

Firemen and National Guardsmen were called out to quell rioting that broke out in Washington following the news of the assassination of Dr. Martin Luther King, Jr., April 6, 1968. (AP Photo)

AP080718016100

National Guardsmen were called out to quell rioting that broke out in Washington following the news of the assassination of Dr. Martin Luther King, Jr., April 6, 1968. (AP Photo)

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ADVANCE FOR WEEKEND OF MAY 24-26 In this June 10, 1964 file photo, Dr. Martin Luther King, Jr. gives a young picket a pat on the back as a group of youngsters started to picket St. Augustine, Fla. (AP Photo, FILE)