President-elect Donald J. Trump is keeping secret the names of the donors who are funding his transition effort, a break from tradition that could make it impossible to see what interest groups, businesses or wealthy people are helping launch his second term.Mr. Trump has so far declined to sign an agreement with the Biden administration that imposes strict limits on that fund-raising in exchange for up to $7.2 million in federal funds earmarked for the transition. By dodging the agreement, Mr. Trump can raise unlimited amounts of money from unknown donors to pay for the staff, travel and office space...