Despite being out of office for more than four months, Republican lawmakers are still making the health of former President Joe Biden a priority.

This week, House Oversight Committee Chair James Comer sent letters to Biden's physician, Kevin O'Connor, and three former White House aides, demanding that they testify before the committee. The letter was sent just days after Biden announced that he has developed stage 4 prostate cancer.

The letters from Comer suggested that they "covered up" his mental decline.

The letters also come as several new books have been released detailing the concerns White House staffers and Democrats more broadly had about Biden's health in the closing months of his presidency.

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"The cover-up of President Biden’s obvious mental decline is a historic scandal," Comer said. "The American people deserve to know when this decline began, how far it progressed, and who was making critical decisions on his behalf."

Biden has insisted that he has the ability to run for a second term, despite a disastrous debate performance that ultimately led him to drop out of the race. His wife, Jill Biden, echoed those sentiments during a recent interview on "The View."

“The people who wrote those books were not in the White House with us, and they didn’t see how hard Joe worked every single day. I mean, he’d get up, he put in a full day, and then at night he would—I'd be in bed, you know, reading my book—and he was still on the phone, reading his briefings, working with staff. I mean, it was nonstop,” she said.