NEW YORK -- New York candidates for Congress are using Monday as their final full day on the trail to deliver closing messages before Tuesday primaries, where an energized progressive wing is confronting established Democratic figures.

The contests serve as key tests of Mayor Zohran Mamdani's influence, showing whether the young democratic socialist can harness momentum from last year's campaign to alter the makeup of the city's House delegation.

He has actively backed his trio of preferred House contenders by appearing in campaign videos and joining U.S. Sen. Bernie Sanders at a rally last week to energize supporters right before voting begins.

"The party of the past will not be what leads us into the future. We need a Democratic Party with backbone," Mamdani said.

At the same time, in a high-profile contest, Jack Schlossberg, the 33-year-old grandson of former President John F. Kennedy, seeks to use his family legacy and strong online presence to win a House seat covering sections of Manhattan.

Yet the Kennedy descendant faces stiff competition from Alex Bores, a state Assembly member central to a Silicon Valley funding battle over his ideas to oversee artificial intelligence, and Micah Lasher, another state Assembly member with extensive New York government experience and support from many state Democratic leaders. George Conway, an attorney once married to a senior Trump adviser who later became a critic of the president, is also running.

During the campaign's final phase, Schlossberg appeared with David Letterman, longtime host of "The Late Show with David Letterman." His mother, Caroline Kennedy, produced a campaign spot on his behalf. Lasher greeted voters on the streets. Bores issued a spot warning about AI risks and emphasized the large sums Big Tech interests are pouring in to fight his candidacy.

Mamdani has stayed neutral in that contest.

Instead, he has concentrated on three additional House races, two of which involve sitting members facing challenges.

Darializa Avila Chevalier, a democratic socialist lifted by the mayor's backing, is taking on U.S. Rep. Adriano Espaillat, the first Dominican American elected to Congress from a district spanning northern Manhattan and part of the Bronx.

Espaillat has highlighted old social media posts by Avila Chevalier from her twenties to paint her as unprepared. Avila Chevalier, during a recent debate, expressed regret over those posts and apologized for one crude remark about former Vice President Kamala Harris.

Former city Comptroller Brad Lander received the mayor's support in his challenge to U.S. Rep. Dan Goldman, a fellow Democrat.

Lander, who joined the crowd at a festive City Hall event marking the Knicks NBA title win on Thursday, has stressed his partnership with the mayor, while Goldman, who withheld an endorsement from Mamdani during the mayoral race, has focused attention on his legislative record in Congress.

Mamdani is also backing Claire Valdez, a former state Assembly colleague and democratic socialist ally, in her effort to defeat Brooklyn Borough President Antonio Reynoso for the seat being vacated by retiring U.S. Rep. Nydia Velazquez.

Reynoso and Valdez are both progressives with overlapping positions, though Valdez has positioned herself as a likely Mamdani partner in Washington.