In an analysis of the Harry Reid flap, Jeff Zeleny of The New York Times makes a similar point:
When he spoke to some black audiences, Mr. Obama’s consonants tended to linger a bit. He would speak with a certain staccato and rhythm – particularly in churches – that he had not used when addressing white audiences in Iowa or New Hampshire.
This, of course, is hardly unique to Mr. Obama.
Other black politicians have followed a similar pattern. And the same is true for many white politicians – Bill and Hillary Clinton, for example – when a Southern accent suddenly is more pronounced during a campaign speech below the Mason-Dixon Line.
For Mr. Obama, the pattern began well before he started running for president. It was noticeable as he gave speeches across the country as a freshman senator. One day in 2005, after he delivered an address in Detroit at an anniversary celebration of the N.A.A.C.P., I asked Mr. Obama about the differences.
“I know if I’m in an all-black audience that there’s going to be a certain rhythm coming back at me from the audience. They’re not just going to be sitting there,” Mr. Obama told me. “That creates a different rhythm in your speaking.”