A top former official of the Biden administration is reportedly cooperating with a GOP-led probe into the final months of former President Joe Biden’s time in office, the first breakthrough that lawmakers have had after four previous testifiers refrained from speaking. Ron Klain, the former president’s chief of staff who left his role in February 2023, is said to be cooperating with an investigation led by the U.S. House Oversight Committee, which is exploring whether aides to Biden knew about his mental decline and performed presidential functions without his knowledge. The committee had previously sought testimony from other members of...