OXON HILL, Md. — In a return to the national political stage, Gov. Chris Christie of New Jersey sought Thursday to both ingratiate himself with conservative activists and press them to broaden the appeal of the Republican Party, warning that “we’ve got to start to talk about what we are for and not what we are against.”

The consumer spending slump and tightening credit markets are triggering a widening wave of bankruptcies in American retailing, prompting thousands of store closings that are expected to remake suburban malls and downtown shopping districts across the country.