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Mark McClellan, the administrator of the Centers for Medicare & Medicaid for less than a year, is being called a top candidate to replace Health and Human Services Secretary Tommy Thompson, who announced his resignation Friday. A physician, McClellan previously led the Food and Drug Administration.

Former House Speaker Newt Gingrich, a Republican who represented Georgia, and outgoing Sen. John Breaux (D-LA), the outgoing also are said to have shown interest in the job. In October, Gingrich was named a co-chair of the National Commission for Quality Long-Term Care.

HHS Deputy Secretary Claude Allen is another name being circulated as a possible successor to Thompson, the former governor of Wisconsin. HHS employs more than 60,000 people and has a $500 billion annual budget.