It is not just Donald Trump who believes South Korea is free-riding on the alliance protection by the US
Dr Seung-young Kim writes a column in The Chosun Ilbo, a leading daily newspaper in South Korea about George F. Kennan’s recommendations for US troop withdrawal before and during the Korean War
"George Kennan, the leading American strategist during the early Cold War, consistently recommended the withdrawal of US forces from South Korea before the outbreak of the Korean War as the Director of Policy Planning Staff in the Department of State. After the outbreak of the war, he recommended a firm initial military response to recover the status quo before the war, but recommended to exert diplomatic efforts to achieve expedient withdrawal of US forces from Korea. His recommendations were in tune with Pentagon's strategy before the war, while it was advocating such a withdrawal due to tight constraint imposed on US defence budget.
South Korea's value as a US ally has increased dramatically since the end of the war with growth of its military and economic capabilities. Recently, the new 'challenges' posed by the rise of China in the 21st century has also enhanced South Korea's value as an ally for the United States. Yet, in recent US presidential election campaign, Donald Trump has harshly criticized South Korea for 'free-riding' on US protection. In academic debates on policy issues, Kennanesque strategy is still discussed as a viable option in the United States. George Kennan’s diaries and papers, made recently available after his death in 2005, make us to consider strength and prospect of US alliance commitment to Korea amid rapid development of North Korean nuclear weapons capabilities. "
The Full article can be found here (Written in Korean)