A small, tight-knit group in former President Joe Biden’s inner circle was running the White House like a “politburo,” and they were the “ultimate decision-makers” as Biden’s health and cognitive function continued to decline, according to the authors of a bombshell new book.

This group, dubbed the “politburo,” included a coterie of seasoned political veterans, including Mike Donilon, Steve Ricchetti and Bruce Reed — but also family members such as first lady Jill Biden and the president’s son Hunter, the authors of “Original Sin” claim.

“In terms of who was running the White House, it’s a small group of people that have been around,” “Original Sin” author Alex Thompson told PBS’ “Washington Week” on Friday. “Some people within the administration called them the Politburo. That’s the term we used in the book.”

Former White House chief of staff Ron Klain was at times part of the “politburo,” as was former senior adviser to the president Annie Tomasini. Also on the “politburo” was the first lady’s former top adviser and “work husband,” Anthony Bernal, whom The Post previously reported created a toxic workplace environment.

“And Joe Biden himself also is part of this. Joe Biden is not like — it’s not ‘Weekend at Bernie’s,’ right?” said co-author and CNN anchor Jake Tapper, referring to the movie about a dead guy who is wheeled around as part of an elaborate ruse.

“He has some purchase here. He has some agency. And he’s aware of some of what’s going on.”

Tapper added: “He’s aware of the fact that they are keeping the cabinet away from him, they are keeping some White House staffers away from him.”