But mindful as much of the party’s prospects in 2020 as of inflicting short-term pain on Mr. Trump, party leaders are divided on how quickly and aggressively to act. Some in the party fear that if they fail to build an adequate public rationale first, Mr. Trump would paint the majority as cravenly abusing its authority, undercutting Democratic efforts to project a steady-hand alternative to the Republicans…

Further complicating matters, Democrats are preparing an onslaught of investigations through numerous committees should they gain control. They must weigh how to prioritize file cabinets’ worth of unaddressed document requests and investigative leads on issues such as Russian election interference, presidential business profits from foreign governments, cabinet corruption allegations and hurricane relief.

“You should not rush into this thing,” said Representative Bill Pascrell Jr. of New Jersey, a Democrat on the Ways and Means Committee who has pushed Democrats to take on the tax issue. “I don’t think you are here to bury anybody. You are here to find the facts.”