A high-level defector from Kim Jong-un’s regime has sent a letter to President Trump warning that he has been “tricked” into believing the North Korean leader will ever denuclearize and that Washington should instead ramp up a “psychological warfare campaign” aimed at inspiring North Korea’s elites to replace the young dictator from within.

The U.S. should simultaneously impose “all-out sanctions” against Pyongyang and be prepared to carry out a “preemptive strike” against Mr. Kim’s nuclear sites, according to the letter, a copy of which was obtained by The Washington Times.

The warning comes as the White House seeks fresh momentum for Mr. Trump’s historic personal diplomatic outreach to Mr. Kim in the face of a slew of provocative military moves, rhetorical outbursts and more than a dozen ballistic missile tests by Pyongyang in recent months.