WASHINGTON (TNND) — Allegations of a cover-up regarding President Biden's health have led to several individuals being called to testify before lawmakers.

Former President Biden spoke publicly for the first time since his cancer diagnosis, expressing optimism about his health.

"The greatest honor of my life was for four years being the commander in chief," Biden said. He added, "The prognosis is good. We're working on everything. It's moving along. I feel good."

Biden's health and mental fitness have come under scrutiny following a recent book alleging a cover-up of cognitive decline during his presidency and his decision to run for a second term.

When asked about these reports and criticism from some Democrats, Biden responded, "Why didn't they run against me then? Because I would have beat them."

On Capitol Hill, the House Oversight Committee has launched a probe involving Biden's doctor, Kevin O'Connor, and four top aides. They are communicating with GOP lawmakers about potential testimony, including the use of an autopen for signing documents in Biden's final months in office.

Rep. James Comer, R-Ky., chairman of the House Oversight Committee, said, "We want to know who gave them the authority to do that, and we want them to walk us through the exact process of how major items of huge legal consequences like pardons and executive orders ended up being placed in the autopen and having Joe in Biden's signature forged on there."

Biden's team has denied any wrongdoing. Meanwhile, new questions have arisen following interviews with Secret Service agents.

Sen. Josh Hawley, R-Mo., claimed, "The Secret Service whistleblower actually was assigned to Biden and he told me that Biden used to get lost in his closet in the morning in the White House."

The Senate Judiciary Committee has announced its own investigation, with a hearing scheduled for June 18.