In a realistic sense, that is sort of a waste. The reason it's not necessary to appeal to moderate democrats is that they do not EVER defect in numbers high enough to matter much in elections. 

The demographic that is important to woo are non-aligned voters (independents). Capture THAT block and you don't need to win over any 'Crats. 

So the central point RB made (that DJT is a polarizing force who loses a small but significant segment of voters just by running) is good - it holds true but applies more to independent voters than 'Crats who are on the fence. 

The natural progression of most who change their votes from Democrat to Republican when they're 'Crats, is they change parties first (to independent), then vote for conservatives (Republicans) if no conservative Independents are running. They don't often stay in the Democrat party when they switch their votes (unless they want to please a spouse by lying).

A large segment of democrat party voters changed to independent status in the last few years. A bunch of Latinos, blacks and females made the switch and by all appearance won't be back any time soon. 

DJT's weakness with those same demographics is problematic. It might not be insurmountable but it's a concern.