Moderates normally would vote against Trump despite a good economy because he’s an enormous prick and terrible human being.
But moderates also will not have any part in taking the Country to hard left crazy town just because Trump is the worst. That’s the Democratic Party’s problem.
When the Democratic Presidential candidates stand on the debate stage and say, for example, that they want to legalize undocumented border crossings and provide free healthcare to those who do make it across, they wound the Democrats’ 2020 chances greatly.
Stuff like that flies so hard against what most moderates (and probably even most people in general) would consider to be common sense that they’d rather let the enormous prick and terrible human being remain in office than see that actually happen.