But even before impeachment, House Democrats were gaining little traction with policy bills that withered in the Republican-controlled Senate. Polls have shown their proposals to be popular, but they have been routinely overshadowed in the news by Mr. Trump.
There is little doubt that impeachment will become a singular obsession in the political world and dominate news coverage for as long as the inquiry is underway. A few early polls on impeachment suggest that public support for the inquiry is somewhat stronger than opposition to it, but those numbers could easily change in either direction as the process unfolds.
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Diane Feldman, a Democratic pollster, said it would be difficult for the party to communicate with voters on issues besides impeachment for the duration of the process. But candidates up and down the ballot had to try to drive a message about policy all the same, she said.
“I think it’s worth the effort, but it’s a long shot,” Ms. Feldman said. “That we not put all of our eggs in the impeachment basket seems to me extremely wise.”
However, Ms. Feldman said, the impeachment process could also “add some clarity to risks that Trump presents to our national security and foreign policy” and sharpen the overall Democratic case against his re-election.
The task of balancing impeachment against policy priorities will be especially delicate for lawmakers elected last year, including dozens who won narrow victories in historically Republican districts. Democrats are defending a sizable number of seats that Mr. Trump carried in 2016, in parts of the country like upstate New York, Oklahoma City and northern Maine, where the impeachment issue is likely to stir backlash.