Research has shown that someone with a poor credit history is not automatically a poor job prospect. Nevertheless, millions of Americans who have emerged from the recession with medical debts or a record of late payments are at risk of being denied jobs by companies that use credit histories to screen applicants. Several states have placed limits on this practice. But until the federal government engages the issue more aggressively, employers will consign otherwise qualified applicants to a kind of pariah class that gets shut out of the job market.