“North Korea fired off some small weapons, which disturbed some of my people, and others, but not me,” Mr. Trump wrote as he was traveling in Japan. “I have confidence that Chairman Kim will keep his promise to me, & also smiled when he called Swampman Joe Biden a low IQ individual, & worse. Perhaps that’s sending me a signal?”

Asked by Chuck Todd, the NBC host, about the president “essentially siding with a murderous authoritarian dictator over a former vice president of the United States,” Ms. Sanders replied, “The president’s not siding with that.”

She added: “I think they agree in their assessment of former Vice President Joe Biden. Again, the president’s focus in this process is the relationship he has and making sure we continue on the path towards denuclearization. That’s what he wants to see and that’s certainly what the people in this region want to see.”