As President Donald Trump prepared to take office nearly four years ago, his predecessor had a warning. President Barack Obama advised Trump that North Korea’s ballistic missile and nuclear weapons programs would be the most pressing danger he would face. At a military parade in Pyongyang earlier this month the North Koreans unveiled what CNN described as the “world’s largest liquid-fueled intercontinental ballistic missile.” It was a worrisome reminder that the threat of North Korea’s nuclear weapons program remains intact and, in some respects, has grown since Trump’s inauguration in January 2017.

Obama’s warning did not go unheeded. The Trump administration attempted to convince Kim Jong-un, a murderous tyrant, to give up his nuclear aspirations. But that effort, like previous American initiatives, has clearly failed. Why? The simplest answer may be that there is nothing the U.S. or its allies can do to dissuade Kim. Still, it is worth revisiting the story of the past four years to understand what exactly the Trump administration tried to do. 

For that explanation, we turn to Battlegrounds: The Fight to Defend the Free World, a new book by Lieutenant General (ret.) H.R. McMaster. Full disclosure: McMaster is Chairman of the Board of Advisors for the Center on Military and Political Power at the Foundation for Defense of Democracies (FDD), the same think tank that employs me. And I’ve advised McMaster, who cited my work on jihadism in Battlegrounds. 

McMaster took over as Trump’s National Security Advisor in February 2017, after his predecessor, Gen. Michael Flynn, was ousted just weeks into the new administration. From the outset, McMaster had to navigate turbulent political seas. He explains how rising isolationist sentiment, especially throughout Trump’s political base, complicated his job. In 2016, for instance, the Obama administration reached an agreement with the government of South Korea to deploy the Terminal High Altitude Area Defense (THAAD) missile system. This “seemed like a logical response,” McMaster writes, to the provocative tests performed by Pyongyang, which threatened South Koreans and Americans living in or stationed on the Korean Peninsula.