Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE will give a speech Thursday in New York about "where we go from here" as he continues his presidential campaign despite Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE's hold on the Democratic nomination.

It's Sanders's first campaign event since he addressed supporters in a live video last Thursday after the final 2016 primary.

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In that video, he pledged to work with Clinton to defeat Republican Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE and to "transform the Democratic Party." But he refused to endorse the former secretary of State, who has secured enough delegates to win the nomination at the party's national convention in July

Instead, Sanders had been signaling that he would devote his energy to leaving his mark on the party's platform; he still has a formidable number of delegates and supporters who will attend the convention.

A campaign aide reportedly denied Thursday's speech would include a concession:

Sanders aide, asked if speech tomorrow will have big concession/endorsement news: "No." — John Harwood (@JohnJHarwood) June 22, 2016

Sanders previously tried to put a plan in motion to convince superdelegates to abandon Clinton and jump on board his campaign. But his team declared that effort was over last week, and Sanders acknowledged that he is largely out of options in an interview Wednesday with C-SPAN.

"It doesn't appear that I'm going to be the nominee, so I'm not going to be determining the scope of the convention," Sanders told the network.

The Vermont senator, however, will play an important role in the party's efforts to unify Democrats behind Clinton. A Bloomberg poll found that almost half of his supporters said they won't vote for Clinton, so his endorsement would be vital for the presumptive nominee. While his supporters have suggested him as a vice presidential candidate, multiple news outlets report that Clinton has begun vetting others.

Sanders told C-SPAN that Clinton should pick "the most progressive running mate that she can find," adding that it would be a "terrible mistake to go to a candidate who has roots in Wall Street or is backed by Wall Street."