I wish I shared your optimism, however if the last 3 years have taught us anything it's that..
There's a good chance the Dems will fail to put up a suitable candidate capable of beating him.
The election campaign will be an absolute shitshow of lies, false claims, bots and fake news.
A large part of the country will support him regardless of the lies and what he says or does. It's a cult at this point now.
There are many Republican 'never Trumpers', however they are all also 'never Democrats'. They'll hold their noses and vote Red. The left will stay at home if the Democrat candidate is shite.