The Department of Health and Human Services on Wednesday returned fire at House Oversight Committee chairman Darrell Issa (R-Calif.) over his threat to investigate HHS Secretary Kathleen Sebelius for “false and misleading” testimony to Congress.

In a letter obtained exclusively by The Hill, HHS assistant secretary for legislation Jim Esquea wrote a measured and clinical point-by-point rebuke of Issa’s charges that the secretary sought to mislead Congress about testing and security issues surrounding HealthCare.gov.

“You made the very serious charge that the Secretary’s testimony was ‘false and misleading,’” Esquea wrote. “We have reviewed your claims carefully. As explained below, they are not supported by the record and are incorrect.”

Caught in the dispute is MITRE Corp., a contractor working to assess security issues with the ObamaCare website.