The 20-Somethings Who Help the 70-Somethings Run Washington

When an alarmed Representative Kevin McCarthy, the minority leader, called the White House on Jan. 6, 2021, demanding to know why the president of the United States had suggested he was coming to the Capitol while Congress met to certify his election defeat, the person on the other end of the line had just turned 25 years old.

“I said, ‘I’ll run the traps on this,’” Cassidy Hutchinson, now 26, testified this week before the House select committee investigating the Jan. 6 attack, recalling what she had told Mr. McCarthy, Republican of California. “I can assure you, we’re not coming to the Capitol.”

Ms. Hutchinson’s two hours of testimony provided a riveting account of President Donald J. Trump’s mind-set and actions the day of the mob attack and situated the young aide — an assistant by title, but a gatekeeper in practice — at the very center of some of the most sensitive conversations and events of that day.