President Trump downplayed the leak of military plans on a commercial messaging app, characterizing it as a minor transgression. He stood by his national security adviser, Michael Waltz, who inadvertently added a journalist to a group chat with other members of the president's inner circle. Senate Democrats expressed outrage, while most Republicans reacted with indifference. In other news, Ukraine and Russia agreed to stop fighting in the Black Sea, but the deal extracted no major concessions from Russia. Frank Bisignano, the nominee to lead the Social Security Administration, vowed not to seek privatization of the program. Doctors in West Texas are seeing measles patients whose illnesses have been complicated by alternative therapies endorsed by vaccine skeptics.