We are not sure who Thomas Parker is.
Perhaps AP thinks two wrongs make a right. In any event, the original quote was by Theodore Parker as we reported at the second link below.
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From the next paragraph in the AP report
"It was not us that thought he said it, it was many people that believed - rightly so — that he said it," press secretary Robert Gibbs said.
If you said "I have a dream" does that mean from now on everyone should attribute that quote to you?
Back to the AP article:
Parker's adherents note the Transcendentalist and Unitarian minister wrote this in his 1853 treatise "Of Justice and the Conscience": "I do not pretend to understand the moral universe; the arc is a long one ... And from what I see I am sure it bends towards justice."
Jamie Stiehm, writing in The Washington Post on Saturday, said crediting King but not Parker "goes beyond the beige."
One commenter said, "this gives a whole new meaning to "lying like a rug."
Link here and here.