WASHINGTON — The State Department has hired an alarming number of law-enforcement agents with criminal or checkered backgrounds because of a flawed hiring process, a stunning memo obtained by The Post reveals. The background problems are severe enough that many of the roughly 2,000 agents in State’s Bureau of Diplomatic Security can play only limited roles in agency efforts to police bad conduct and prosecute wrongdoers. The problems in the bureau are the latest revelation in an exploding scandal that also involves accusations that members of former Secretary of State Hillary Rodham Clinton’s security detail |