The testimony came from an aide to Mr. Meadows, Cassidy Hutchinson, a 26-year-old who was not mentioned in his book, The Chief’s Chief, but whom former White House and Capitol aides said played a key role in the office. of. In the run-up to the last days before Trump’s supporters stormed the Capitol to stop President Biden’s victory certification, Mr. Meadows spent much of his time on the phone while Trump administration officials hailed Trump possibility of violence.