After the 2016 election, Democratic leaders reached an all but unanimous conclusion: To defeat President Donald Trump in 2020, they would have to do more than condemn his offensive behavior and far-right ideology, as Hillary Clinton had done. They would need, above all, to promote a clear and exciting agenda of their own.

As Democratic presidential contenders pushed campaigns built on big ideas, House Speaker Nancy Pelosi resisted a chorus of calls for impeachment, even from some of her party’s leading 2020 candidates.

Yet 13 months before the next election, Democratic leaders are now steering into a protracted, head-on clash with Trump. By seeking the Ukrainian government’s help in tarring former Vice President Joe Biden, Trump left them no choice, they say, but to pursue an impeachment inquiry that could consume the country’s attention for months.

Pelosi has indicated she aims to move the process along with haste, in part to avoid an election-year conflagration, but the exact course of the inquiry is impossible to foresee.

All 19 Democratic presidential candidates now support the impeachment inquiry, and many Democrats are optimistic that voters will, as well, because Trump is so unpopular and the allegations against him are grave and easily grasped.

But there is also a general recognition, at every level of the Democratic Party, that impeachment could complicate their candidates’ efforts to explain their policy ideas to the country and persuade voters they have a vision beyond ousting Trump. The party has been disappointed too many times, its leaders say, by betting that Trump’s violations of political and cultural norms would bring about his downfall.

On Friday evening, Pelosi declared at a conference of New Jersey Democrats in Atlantic City that she would not allow the 2020 election to become a campaign about impeachment. Insisting the inquiry “has nothing to do with the election,” she said the campaign would be fought on other terms.

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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