Why Singapore summit may define Trump's foreign policy legacy

US Secretary of State Mike Pompeo asserted on Sunday that North Korean leader Kim Jong-un's vow to destroy his nation's key nuclear testing site "is a good first step" in preparations for the landmark June 12 Singapore summit between US President Donald Trump and Kim. With positive mood music currently surrounding the Trump-Kim session, Korea offers the potential to become the US president's first big foreign policy win.

Any final, comprehensive deal between Washington and Pyongyang is possibly years away. Yet, it is already clear that it would be a remarkable achieve…