Republicans grill Obama's Medicare-Medicaid chief

Previewing the partisan healthcare battle to come next year, the Obama administration's new head of Medicare and Medicaid squared off against irritated Republicans on Capitol Hill for the first time Wednesday in a renewed debate over the healthcare overhaul.

Dr. Donald Berwick, whom President Obama appointed in July without Senate confirmation to help lead implementation of the new healthcare law, told lawmakers that repealing the legislation — as the GOP has vowed to do — would be a major mistake.