to keep america secure. >> after their first summit last year, trump tweeted that north korea was no longer a nuclear threat. let's go straight to the white house. correspondent sarah westwood standing by. sarah, president trump today firing off some fresh tweets on north korea. what is he saying? >> reporter: well, ryan, president trump is showcasing what is likely to be the primary message from the u.s. to north korea at the summit. and that's all about the prosperity that kim jong-un could secure for his country, if he were to denuclearize. trump is pressing that issue on twitter this morning, writing, chairman kim realizes, perhaps better than anyone else, without nuclear weapons, his country could fast become one of the great economic powers anywhere in the world. and he goes on to say, because of its location and people and him, it has more potential for rapid growth than any other nation. of course, white house officials had hoped to use the backdrop of vietnam, which was once hostile toward the u.s., as an example of the kind of economic revival