I think a large factor in Trump's success was less that the electorate wanted him than that they didn't want Hilary Clinton - the least worst option was what they had to go with.
So a similarly large factor will be the ability of the Democratic nominee to offer something different and better to Trump, and make the electorate believe it.
An uphill struggle, but not an unwinnable ne, given that this is politics, and President Trump has shown himself wilfully proud of his position in not understanding what politics is about - and that could cost him the presidency next time round.