The time for North Korean diplomacy or war

North Korea has not abandoned its nuclear weapons program, continues to test missiles and is being blamed for the death of Otto Warmbier, a U.S. student arrested in North Korea and sent home in a coma.

The Atlantic's Mark Bowden has called North Korea "the worst problem on earth" — it already has the power to destroy Seoul (home to 24 million), is developing missiles to hit Los Angeles, and its collapse could cause the biggest refugee crisis since World War II. President Trump has tried to enlist China to help control the rogue regime but tweeted that "has not worked out."

So before North Korea can nuke L.A., or kill millions on the Korean peninsula, what should the U.S. do? We asked 5 experts on U.S./North Korean issues to lay out the challenge and pick a course of action. Here are their answers:

• Jim Walsh, Senior Research Associate at MIT's Security Studies Program: Negotiate or else
• James Poulos, foreign policy author, contributing editor at American Affairs: Wage cyberwar on North Korea's infrastructure
• Van Jackson, former Defense Department adviser focused on the Asia-Pacific: Escalation could lead to nuclear war
• Wendy R. Sherman, former undersecretary of State for political affairs: Full-court diplomacy (even secret talks with North Korea)
• Kurt Campbell, former assistant secretary of State for east Asian and Pacific affairs: A Trump Nixon-to-China moment in North Korea