After a week of jarring markets with announcements aimed at making homes more affordable, the president swiveled to another consumer burden: the cost of carrying a credit card balance from one month to the next. This time, his social-media missive pushed a slew of card issuers led by JPMorgan Chase & Co., Capital One Financial Corp. and Citigroup Inc. into the crosshairs. Card interest rates — hovering above 20% in recent years — have become a target of lawmakers on both sides of the aisle, with bills popping up and meeting stiff resistance from the industry.