Populism is not so much a political stance (as "conservatism" is, for instance) as it is a political tactic. Meaning it can be used equally well by either side of our current American political divide.
There is a misplaced assumption that because African-Americans are more likely to be unemployed or poor, the policies designed to create jobs will benefit them evenly or in proportion to their disadvantage.
The Frank and Dodd regulatory reform bills are terribly drafted provisions which will strike a death blow to "main street" lenders and hand over a multi-trillion dollar mortgage market to a few large financial institutions.
Geithner is a continuing liability for this President. By stepping down, he can rightly claim some successes, while also presenting an opportunity for Obama to appoint a Treasury Secretary who fights for Main Street.