Inflation was too high. Turnout was too low. President Biden stayed in the race too long. His summer polling deficit was too steep to overcome.

The excuses for Kamala Harris’s loss are piling up, but they mask a deeper, more devastating reality: Democratic Party leaders did not listen deeply to and earn the trust of young voters, who could have helped her prevail in Michigan and other swing states. As a pollster who focuses on the hopes and worries of these Americans, losing to Donald Trump — not once but twice — represents a profound failure. Ms. Harris’s campaign needed to shift about one percentage point of voters across Pennsylvania, Michigan, and Wisconsin to secure the presidency, but instead struggled in college towns like Ann Arbor, Mich., and other blue places. Think about that: Flipping just one in every hundred voters would have stopped the likelihood of mass deportations, tax cuts for the wealthy, rollbacks of L.G.B.T.Q. protections and the reversal of climate regulations.

This was an eminently winnable race. Ms. Harris’s campaign rollout, convention speech, and debate performance captured the imagination of many young Americans, offering a vision of leadership rooted in progress and aligned with their values. Yet in the critical weeks that followed, her campaign struggled to close the deal with members of Generation Z who saw Ms. Harris as more of the same presidency that they felt let down by. Some of us saw her poll numbers and trajectory this fall and warned about what was coming; we were dismissed as “bed wetters.” But can anyone really describe her vision and ideas that would have made a tangible, affirmative difference in the lives of young people, relieving their economic stress and advancing their desire for a just society, a peaceful world and a healthy planet? “Not being Trump” was never going to be enough.

Data from multiple sources warned against an overreliance on abortion messaging in the closing weeks, emphasizing that it was neither a silver bullet nor a magic wand. But these warnings went unheeded, leaving too many young people — women and men — feeling unheard and misunderstood. Vocal, explicit support for abortion rights seemed to be the way Ms. Harris wanted to differentiate herself from the more moderate tone of Mr. Biden and to rally women, including younger female voters. But many American voters knew in their hearts that she was unlikely to be able to restore Roe and they were voting chiefly on issues and goals that felt more immediate and urgent.

This failure is especially remarkable given that the Biden-Harris administration’s first years delivered significant youth-centered achievements — student debt relief, unprecedented climate investments and meaningful gun safety legislation. Yet these victories were difficult for many young people to see or feel in real time and Mr. Biden lacked the gifts of speechmaking and persuasion to talk about these accomplishments effectively in today’s fractured media landscape. Imagine if Mr. Biden or Ms. Harris had the dexterity and fluency to go on YouTube with Hasan Piker, or on Joe Rogan’s podcast, or other Gen Z destinations and make the case to young Americans about these accomplishments.

Instead, many young voters didn’t perceive the tangible impact of their 2020 vote for Mr. Biden, which not only eroded their faith in the Democratic Party but also deepened their cynicism about government and politics as a whole. This disillusionment left some of them more open to Mr. Trump’s messaging that the current government is ineffective and that he alone could respond decisively to their fears. It left others more open to Jill Stein’s candidacy or the choice of writing in the name of someone they trusted, rather than filling out their ballot for someone they didn’t.