The call from the White House came late in the week. Rep. Paul Ryan was vowing to slash Medicaid in his 2012 budget proposal, the administration strategists explained, and they wanted to have a powerful response ready, complete with poignant stories of Americans who might lose their health coverage under the Republican plan. Within minutes, Elizabeth Prescott was on the case. The coordinator of a vast database of real-life stories maintained by the advocacy group Families USA, Prescott worked through the weekend poring over hundreds of files. Among them were heart-wrenching tales of hardship faced by people whose care is dependent on Medicaid, the joint federal-state health insurance program for the poor and disabled.