South Korean President Moon Jae-in and North Korean leader Kim Jong-un agreed in their April 27 summit to formally end the 1950-53 Korean War this year, replacing the armistice that halted the hostilities with a peace treaty for permanent peace on the Korean Peninsula.
But after his sitdown with Kim in June to discuss the nuclear disarmament of North Korea and the possible opening of new economic deals with the United States, Chang said, Trump "squandered the advantage - he let up the pressure".
The 38 North report comes amid growing questions about North Korea's willingness to live up to the commitments Kim made at the summit, particularly to work towards denuclearization.
In a typical commentary late last week, the North Korean ruling party's daily newspaper, Rodong Sinmun, called Japan "impotent" in the political and diplomatic arena and said Kono was a "political charlatan".
"The commander of US forces in South Korea says North Korea's level of provocation toward the USA changed months before President Trump's summit in Singapore with North Korean leader Kim Jong-un". The Japanese leader could meet Kim at an eastern Russian Federation development forum in Vladivostok in September, where Kim and Putin may hold their summit.
Trump's interest in the issue has put a particularly bright spotlight on Secretary of State Mike Pompeo, who has tried to wring concessions from his counterpart, Kim Yong Chol, a former spy chief viewed by the Trump administration as uncompromising and unable to negotiate outside the most explicit directives from Kim Jong Un.
Pyongyang apparently has a big demand for the USA if the latter wants to keep talking about North Korea's nuclear arsenal.
Trump said last week that USA relations with North Korea "are very good and the process is moving along".
In its Monday edition, North Korea's state website carried a commentary criticizing Washington for its unwillingness to talk about a declaration to end the Korean War. "Our forces in South Korea are stabilizing for Asia", he said.
After an problematic meeting in Pyongyang involving Secretary of State Mike Pompeo and a team of North Korean officials, the North criticized the USA for making unilateral demands of North Korea while ignoring Pyongyang's expectations, with a peace treaty being high on the country's list of demands.
But US officials suspect that it has been used to test ballistic missiles. We have no time limit.
Pyongyang also committed to returning the remains of U.S. soldiers killed during the Korean War.
"Trump has been hit with a strong dose of reality of North Korea's negotiating style, which is always hard for Americans to understand", Duyeon Kim, a Korea expert at the Washington DC-based Center for a New American Security, was quoted as saying by the Post.