How Trump can get the Norks to give up nuclear weapons

North Korea has wanted nukes for a long time now.  Why?  Who are they wanting to defend against?

Trump's offered to end sanctions if the leader of North Korea verifiably gives up its nuclear weapons program.  So to help accomplish that, he should go on TV to promise--in the tongue-in-cheek way that drives Dems nuts--that the U.S. will absolutely defend North Korea from any invasion from...south Korea.

He could make this offer even funnier by adding--again, tongue-in-cheek--"Now if China were to decide, against all logic, to invade you, we couldn't defend you against that, cuz Chinese president Xi is a good friend of mine.  But I'll absolutely promise that the U.S. will defend you against attack by the South!