(The ONE thing that might make sense about Trump's announcement - and this is totally 4D chess that I refuse to ascribe to him - is to motivate Congress to pass something to stymie him. By threatening an EO, they might pass something to take away that option, which would be VERY counterintuitive.)
Or, it could just be a simple ploy to make headlines a week before the primary to take the media's focus away from wall-to-wall coverage of lunatic pipe bomb makers and anti-semites shooting up synagogues.