(NewsNation) — A longtime aide to former President Joe Biden is expected to testify in front of the House Oversight Committee on Thursday over allegations of a cover-up involving his mental acuity and use of an autopen.

Anita Dunn served as senior adviser for communications during Biden's term. Like other former White House officials, she'll face questions about Biden's mental state in the final months of his tenure.

The Republican chairman of the committee overseeing the investigation, Rep. James Comer, R-K.Y., told NewsNation that Dunn's proximity to Biden could provide crucial information.

"These insiders that we're bringing on on the autopen investigation, they were the only ones that had access to Joe Biden for more than a photo-op amount of time," Comer said Wednesday. "And that's

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