This is as silly as calling a 7-7 score in the first quarter a “plateau”. Why get all excited about it - just wait and see like everyone else.
What would you call it if not a plateau? All candidates reach their plateau to start - it is their base. Trump has achieved his base. He now needs to significantly turn up the heat to build on that. How successful he will be depends on his strategy. If he stays focused on Hillary, I think he will be more successful, but I have no idea what his campaign strategy may be.
Trump then should get too excited about all the polls he is leading in?