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CMS Administrator Marilyn Tavenner signed the document, after the agency’s chief information officer at the time, Tony Trenkle, declined to sign off on it, according to testimony.

Administration officials said CMS carefully considered the authorization to operate, which is limited to six months. They said it was appropriate for Ms. Tavenner to sign the document, given the high-profile nature of the project.

But Mr. Issa said the move was unprecedented.

“Prior to further investigative action by the committee, we thought it prudent to write to you and invite you to reflect on your testimony,” he wrote to Mrs. Sebelius. “Should it be necessary to clarify or amend your testimony then we request you do so as quickly as possible.”