What will the political impact of the Obama speech be?

By most accounts (including, admittedly, my own), Obama's speech on race today was significant for the graceful and forthright way that it addressed the issue of race in America. But the impetus for the speech was political, and it is less clear what the political effects of the speech will be. Note from the Gallup tracking poll (pictured below) that Obama's standing in the Democratic nomination race has declined steadily since the videos of Jeremiah Wright's sermons started making the rounds on television news programs last week (I've denoted the timing with the red horizontal line).

Gallup's tracking poll uses a three day rolling sample. Thus, the last day shown (March 17th) included interviews conducted on Saturday, Sunday, and Monday. Tomorrow's release will be the first to include interviews taken after Obama's speech on race (those interviews were conducted this evening), though they will only comprise one-third of the sample. By the end of the week, we'll have survey points with interviews taken entirely after the speech. It will be interesting to see what happens in tomorrow's survey (does the decline level off, or even tick back up a bit?), but especially the following two days. Stay tuned...