Obama wants riots because voters will be frightened and will believe only Obama can restore peace. Clinton was our first black president, after all.
Riots reduce support for Bush president in dead heat with Clinton, Perot Poll shows big lead decreased sharply
May 05, 1992
http://articles.baltimoresun.com/1992-05-05/news/1992126057_1_perot-clinton-bush-president
That may or may not be what he wants, but if there are riots, the independent vote will desert him and he will lose big.