If the triumph of Trumpism is the most important recent development in American political history, then the second most important is the mobilization of liberal and left-wing voters to challenge the president’s authoritarian politics.

This mobilization drove the Women’s March, where a day after Trump’s inauguration, hundreds of thousands came to Washington to protest against his nascent administration. Millions of others joined them in cities across the country — a remarkable demonstration of opposition to a new president. It stiffened Democratic resolve to oppose the president at a time when some of the party’s leaders were looking for bipartisan cooperation. It helped halt the Republican drive to repeal the Affordable Care Act — peeling critical support away from Mitch McConnell, the Senate majority leader — and last year powered an electoral wave that gave the Democratic Party its first majority in the House of Representatives since 2010.

If Democrats can be confident ahead of 2020, it’s because of grass-roots activists who have strengthened the party’s political position time and time again. And yet key Democratic leaders are still reluctant to follow their lead.

[Jamelle Bouie answered your questions about this column on Twitter.]

We’ve seen this in the fight over impeachment. Many Democrats — 36 percen t according to a recent poll from Marist and NPR — want Speaker Nancy Pelosi and other leaders to begin impeachment proceedings. Those who don’t still want Democrats to continue to pursue investigations into the president’s wrongdoing. Constituents in moderate and liberal districts are urging their lawmakers to hold the president accountable for his actions. But Pelosi won’t budge. She and her allies insist impeachment is unnecessary, unpopular and divisive.