AARON MACLEAN: President Park’s spectacular fall means nothing good for U.S.-Korea relations.

Park’s ouster may well be a blow for good government—and it is certainly a credit to South Korea’s still young democracy that the impeachment has proceeded without a rupture in the nation’s constitutional order. Unfortunately from the American perspective, that’s it for good news. The next president, whoever it will be, is virtually certain to be less friendly to the United States and more dovish towards North Korea. The happy moment of a coalition of pro-American governments in Northeast Asia (Abe in Japan, Park in Korea, and Tsai in Taiwan) was brief, and it is over.

The candidate currently leading in the South Korean polls, Moon Jae-in, comes from the liberal opposition and is outspoken in his skepticism of the United States and his support of something like the Sunshine Policy towards Pyongyang, which his party pursued from 1998 to 2008. In second place is Ahn Hee-jung, who has a reputation for being more pragmatic and centrist than Moon. He is currently behind Moon by 15 points in polls, and has to run against him for his party’s nomination. President Park’s party has yet to produce a frontrunner for its nominating process, and, to be frank, may as well not bother.

America’s long-planned and controversial deployment of a sophisticated air defense system to South Korea called “THAAD” began (somewhat by surprise) last week, on what appears to be a timeline accelerated in part by Korean politics and the likely accession to the presidency of the Korean left. The deployment will be complete by summer, and substantially in place even by the time a new president takes office this spring. Like entitlements or government agencies, such deployments are much easier to stop before they begin than they are to roll back once in place. Little else in the years to come is likely to be easy.

SecState Tillerson may have to adapt the old North Korean policy of “strategic patience” to South Korea.