A top former aide to former President Joe Biden testified behind closed doors Tuesday for more than four hours as part of the House Oversight Committee’s investigation into his mental fitness to serve and his White House’s use of an autopen, confirming she was authorized to use the automatic signature device while pushing back on concerns about alleged manipulation or malfeasance. Neera Tanden, who served as director of the White House Domestic Policy Council, explained in her opening remarks Tuesday that she was given authority to wield the autopen. She said she “was responsible for handling the flow of documents...