U.S. President Donald Trump’s abrupt decision to shorten this year’s Ulchi Freedom Shield (UFS) exercise revived an old anxiety in Seoul. What happens when Washington changes the terms of South Korea’s security in ways Seoul cannot fully control?

Trump linked the move to President Lee Jae Myung’s alleged refusal to support U.S. military efforts against Iran and again invoked his “good relationship” with North Korean leader Kim Jong Un.

The decision came without prior consultation with Seoul as Lee’s government tries to complete the transfer of wartime operational control (OPCON) and pursue a nuclear-powered attack submarine.

South Korea has faced