SEOUL, South Korea — The foes of South Korea’s likely new leaders have called them blindly naïve, closet North Korea followers and anti-American — an unsettling accusation in a country where the alliance with Washington has been the military bedrock for seven decades.

Now, after being out of power for almost 10 years, the South Korean liberal opposition is on the verge of retaking the presidency with the historic court ruling on Friday that ousted its conservative enemy, President Park Geun-hye, who had been impeached in a corruption scandal.

The liberals’ presidential hopeful, Moon Jae-in, wants a profound change in the country’s tense relations with North Korea, pushing outreach and dialogue. He also is deeply skeptical of the hawkish stance embraced by the conservatives and South Korea’s most important defender, the United States.

Mr. Moon and his liberal partners are especially worried about a new antimissile shield the Americans are installing in South Korea, citing China’s fury over it and warning of a standoff reminiscent of the Cuban Missile Crisis.