WASHINGTON — In 2016, Michelle Obama’s words became the Democrats’ defining creed to counter Donald J. Trump’s battering ram of a presidential campaign: “When they go low, we go high.”

Two years later, the appeal of “high” seems low.

As much as any policy tensions or messaging debate within the party, this question of tone — of how to combat Mr. Trump effectively without slipping into a pale imitation — is perhaps the central divide of this Democratic moment (and the next one, with the 2020 campaign looming).

How will Democrats choose to revise Mrs. Obama’s sentence, with Mr. Trump heaving insults from the White House and the rally stage — his pre-midterm bully pulpit?

“When they go low, we kick them,” Eric H. Holder Jr., the former Obama administration attorney general and a possible 2020 candidate, said this week.