Both moderate and more left leaning Democrats, electable in different districts, can still provide votes to counter Trump if elected to Congress.

The concept of the big tent works for the Democratic Party. Some districts, such as in New York City can elect candidates who are pretty far to the left. They likely would not win elections in most districts, but their voice could still be welcome in the big tent. Just about all Democrats, whether left or moderate still provide the votes needed in Congress to put guardrails on dangerous dictatorial tendencies of Trump.