Romney has been known to dip into literary language occasionally, especially when he's trying to illustrate a point of history.
The facts seem to be that Romney's father put himself at political risk to march on behalf of civil rights; Mitt and Scott Romney may have heard, as young men, that his father marched "with" MLK in the sense that the preposition is used by a politician who says he "stands" with workers... that Romney's efforts to explain himself were pedantic and, judging by the response, easily mockable... and that, so far, Iowans don't seem to be hearing about this all that much from their own press...
The Kerry comparisons have to hurt, though.
Read it here.
Actually, there is plenty of testimony from eyewitnesses to the effect that George Romney really did march beside Dr. King on at least one occasion.
This is classic campaign nonsense from the MSM. Mitt makes a perfectly reasonable claim, but couches it in metaphorical language. The press takes it literally and cries "inconsistency" which in their pea-brains is the same as pervarication. Then Mitt responds and the goalposts are suddenly moved. Now the problem is that his explanation sounds, to these idiots, too "Clintonian" or "Kerryesque".