Demonsation - Rhetoric - Public Support - Invasion
Since first two steps are already taken care of long ago, we're at the "Public Support" stage. We just need a lot more media attention and articles like this:
BBC News - Sony hack: White House views attack as security issue
NORTH KOREA IS A SERIOUS NATIONAL THREAT!!!!
Then USA can go in and invade it without needing to worry about public opinion or polls.