President Donald Trump and North Korea's leader Kim Jong-un stand on North Korean soil while walking to South Korea in the Demilitarized Zone on June 30, 2019, in Panmunjom, Korea. Brendan Smialowski / AFP via Getty Images fileLater that month, Trump continued to goad North Korea through his tweets. But the argument about how many people could be killed had "no impact on Trump," Schmidt writes. Kelly warned that Trump would need congressional approval for a pre-emptive strike, which "baffled and annoyed" Trump, according to the afterword. Schmidt also writes that it was well-known among senior U.S. officials for several decades that North Korea sought to spy on U.S. decision-makers.