The embattled Transportation Security Administration (TSA) faced its first big test of the season this past weekend, when Americans kicked off their summer travel over Memorial Day. Remarkably for an agency that has lurched from one crisis to another, it passed. Lines were unusually tolerable at airports across the country. But bigger tests are coming. The peak of summer travel is expected to bring long security queues to America’s big airports, due largely to a shortage of TSA screeners and unrealistic predictions about the number of people willing to pay to join the agency’s PreCheck programme, which allows for expedited security checks.