Like many of her fellow citizens, the leader of South Korea’s ruling party was unhappy with President Trump’s threats to destroy nuclear-armed North Korea. But she now says Mr. Trump’s visit this month appears to have made him appreciate more fully the need to peacefully resolve the crisis.

In an interview, the leader, Choo Mi-ae, the chairwoman of the liberal Democratic Party of South Korea and the most prominent woman in the National Assembly, said Mr. Trump’s visit had “actually led to an improvement in our bilateral relations.”

Mr. Trump, she said, had now seen for himself that 25 million Koreans — half the South Korean population — live close to the demilitarized zone that has divided North and South since the armistice that halted the 1950-1953 Korean War.

“All of the growth and prosperity that Korea has achieved after the Korean War is concentrated in this region,” she said. “If there were to be a war, not only would all the lives be lost, but the achievements of Korea would become nothing overnight.”