John Bolton, President Donald Trump's famously hawkish national security adviser, could not have been enthusiastic when his boss crossed into North Korean territory last weekend to make a bit of history with the leader of the Pyongyang regime, Kim Jong Un. For years, Bolton has warned against conciliatory gestures or negotiations with North Korea. Two months before he took his current job, Bolton argued in an op-ed for a preemptive strike on North Korea based on what he called an "imminent" threat. Now Trump's latest diplomatic gambit with North Korea has raised fresh questions about the influence of his national...