For Marco Rubio, the easy part is over. He was confirmed by the Senate as secretary of state with unanimous support, Democrats joining Republicans in praising his acumen and judgment. Now comes the task that will make or break his tenure: retaining the full backing of his new boss,

Senator Marco Rubio warned of China’s growing threat, and he backed NATO but said Europe needed to do more to help protect itself. His friendly, five-hour confirmation hearing seemed to all but guarantee he would be the next secretary of state.