Kamala Harris Needs Young Voters. Her Envoy: Alexandria Ocasio-Cortez.

The New York congresswoman’s foray onto the presidential campaign trail may be a turning point for her and her party.

She leaped into office six years ago as a 29-year-old outsider intent on upending the Democratic establishment, and has used her platform to challenge party leaders at nearly every turn.

But in the waning weeks of the 2024 election, Representative Alexandria Ocasio-Cortez of New York has thrown herself fully behind Vice President Kamala Harris, stepping onto the presidential campaign trail for the first time as an emissary to skeptical young progressives.

The congresswoman has turned out boisterous crowds in Wisconsin, Texas and Pennsylvania, warning college students about the costs of letting older voters decide the outcome. She has taken aim at Jill Stein, the Green Party nominee who Democrats fear could win over disillusioned voters, blasting her as “not serious” and “predatory” in videos on social media, where Ms. Ocasio-Cortez has millions of followers. And she rallied thousands of volunteers in swing states trying to mobilize Latino and union voters.

Ms. Ocasio-Cortez, 35, and Ms. Harris, 60, have never been particularly close. The congresswoman has made no secret of her policy differences with a nominee who is tacking aggressively to the center — often away from the very issues Ms. Ocasio-Cortez values most.

But rather than stoke their differences, the congresswoman has used them to try to burnish her credibility as she seeks to reach crucial segments of their coalition: younger and left-leaning voters who Democrats fear might stay home, many out of fury at the party’s support for Israel in its war in Gaza.

“We elect Kamala Harris and Tim Walz, and we get to see another day in our democracy,” she said Friday night during a stop at Penn State.