I've already been on the record on this board saying Gates was an idiot and the beer summit was stupid but I don't think that had any effect on public action. The public was protesting about Trayvon Martin long before Obama made his comments. You might have a point in Ferguson since the White House formerly commented on it very soon after it happened. On the other hand many have made the case that there was a long history of racial injustice by the Police and a DOJ investigation claimed that the police routinely violated the civil rights of it black people so what happened there could have (I would say quite likely would have) happened anyway.
http://www.nytimes.com/2015/03/04/us/justice-department-finds-pattern-of-police-bias-and-excessive-force-in-ferguson.html?_r=0
He should have NEVER said anything to begin with and he should have NEVER sent Holder to make public comments as well. No matter when the comments were made it should have never been said by a "President" that only fuels the the fire. BTW, I would be willing to be that Sharpton was also send him as well. After all he has been to the White House more than 80 times.