Final answer:
The DNC should target Democratic and swing voters who sometimes vote, as this approach balances potential turnout with the best use of campaign resources on persuadable voters.
Step-by-step explanation:
When the Democratic National Committee (DNC) was targeting voters using their data-driven approach, the most appropriate groups to target would be Democratic and swing voters who sometimes vote. This strategy is based on the principle of maximizing the efficiency of campaign efforts and resources. It emphasizes focusing on those who have a history of turnout but may need extra encouragement or persuasion and those who are undecided or can swing either way, rather than expending resources on those who consistently vote or are highly unlikely to vote.