PALO ALTO, Calif.—The CIA officer who helped orchestrate last year’s diplomatic breakthrough between the U.S. and North Korea said Friday he remains optimistic about progress between the two adversaries, predicting next week’s second summit would be more productive than the first.

Andrew Kim, who retired from the Central Intelligence Agency last year after a 28-year career, acknowledged in a speech here that decades of attempts to negotiate over Pyongyang’s nuclear and missile programs have been marked by missteps and failure.

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