I think you're misunderestimating the degree to which Republicans will blindly vote for Trump simply because he has an (R) after his name on the ballot. Some will, granted. But his presidency has been a unifying factor for the Democrats and a destabilizing one for many Republicans, especially those who aren't hypocrites regarding the deficit and responsible government spending.
Trump's best strategy, I think, is to distract from the Mueller report, corruption within his administration, various international gaffes and cloudy long term economic projections and claim responsibility for the current economic success we're enjoying and of the best ways to do this for him and his supporters seems to be using the "bully pulpit" to try and put a spotlight on any disagreement within the Democratic caucus. Meanwhile Republicans who can't stomach the Retrumplican party are being actively primaried or retiring/switching parties. For people who watch more than Fox News it seems a little desperate.
I think you're right though. The choice ultimately will be Trump or Not Trump and I think "Not Trump" is going to make a compelling case this time around and NO ONE is going think they're sure to win no matter how ridiculous NOT Not Trump acts and campaigns. Fool us once....won't get fooled again!!