John, I agree with your praise of Sharpton as a speaker. It truly is a skill learned in black pulpits. Jesse Jackson has thickened and collapsed in recent years, but in the mid-eighties he blazed. So did Louis Farrakhan.
For a good non-black speaker in the presidential sweepstakes I believe one must go all the way back to John Connally. Ronald Reagan was a special case, succeeding by projecting conviction, warmth and humor, which is a different skill.