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. ... “Department intakes of new . . . officers since the hiring surge a decade ago have reportedly been flawed, with ‘mitigation’ of troubling histories including criminal matters,” according to a December 2012 memo...