For the Pritzker family of Chicago, the 2001 collapse of subprime-mortgage lender Superior Bank was an embarrassing failure in a corner of their giant business empire. Billionaire Penny Pritzker helped run Hinsdale, Ill.-based Superior, overseeing her family's 50% ownership stake. She now serves as Barack Obama's national campaign-finance chairwoman, which means her banking past could prove to be an embarrassment to her -- and perhaps to the campaign. Superior was seized in 2001 and later closed by federal regulators. Government investigators and consumer advocates have contended that Superior engaged in unsound financial activities and predatory lending practices. Ms. Pritzker, a...