SEOUL, South Korea — President Moon Jae-in of South Korea takes every opportunity to describe Kim Jong-un, North Korea’s leader, as a “young and candid” strategist, one who is ready to bargain away his nuclear arsenal to secure economic growth for his impoverished nation.

In doing so, Mr. Moon is attempting something that his predecessors who favored dialogue with the North also tried to do, but failed: changing North Korea’s global image as a regime that simply cannot be trusted.

For decades, it has been an article of faith among Washington’s foreign policy establishment, as well Mr. Moon’s conservative critics at home, that North Korea will renege on any agreement made. For that reason, they say, there can be no substantial concessions to the North in the talks over its nuclear weapons until it takes real steps toward disarming.

That view has contributed to a standoff in the talks between the North and the United States. As Mr. Moon has pushed to deepen ties with Pyongyang, the backlash from his critics has been swift. A major South Korean newspaper this month called him the “chief spokesman for Kim Jong-un,” and an American commentator, quoting Creedence Clearwater Revival, recently referred to him as a “bad Moon on the rise.”