“Trump’s great genius is to try and reduce everyone to his level and approach, and he wants to be able to paint Democrats as single-mindedly bent on his destruction,” said David Axelrod, a Democratic strategist and former top adviser to Barack Obama. “These Democrats didn’t get elected, by and large, to war with Trump. They got elected to try and get some positive things done on issues like health care and economic issues for their constituents, and the notion that on Day 1 they should spend all their energy trying to bedevil him is wrong. Striking the balance is going to be difficult.”

Ms. Pelosi, who hopes to reclaim her post as speaker in the new Congress, has encouraged fellow Democrats in private meetings to resist the urge to leap at Mr. Trump’s every utterance and misdeed — “I don’t think we’ll have any scattershot freelancing,” she told reporters last week — lest they lose focus and play into his hands.

“The message is really, ‘Don’t chase every ball that he throws. We have to show the American people that there’s a purpose behind everything that we do, and it’s not just to get a pound of flesh,’” said Representative Eric Swalwell, Democrat of California.