Bernie Sanders has told supporters that his campaign against economic inequality in the US is "just getting started".
Mr Sanders told a raucous Manhattan audience that he hopes to change the Democratic Party and bolster Democrats running for Congress.
He took something of a victory lap as he reviewed the states he won in the battle for the Democratic presidential nomination, and highlighted the fact that many young people flocked to his campaign over the presumptive candidate Hillary Clinton's.
Mr Sanders did not mention her name, let alone endorse her, as leading Democrats have urged.
"Our goal from day one has been to transform this nation and that is the fight we are going to continue," Mr Sanders, his voice hoarse, told supporters who packed The Town Hall venue near Times Square.
"We have got to make sure that (Republican presidential candidate Donald) Trump is not president. But that is not good enough."
The independent senator received standing ovations as he reviewed his campaign positions, from free health care and college tuition to campaign finance reform.
Mr Sanders urged his supporters to keep fighting inequality and insisting on "forcing open the door" of the Democratic Party to allow it to be run by working Americans, not political elites.
That was a not-so-subtle swipe at a party which he complained had rigged the nominating system in Mrs Clinton's favour.
Mrs Clinton earlier this month clinched the delegates required to carry the Democrats' banner against Donald Trump, with Mr Sanders acknowledging that he would not be the nominee.
Mr Sanders has been signalling the transition of his movement from a presidential run to one aimed at bolstering like-minded Democratic candidates for Congress and offices up and down the ballot.
He is travelling to Syracuse, New York, on Friday to hold a rally with congressional candidate Eric Kingson, who is seeking the Democratic nomination in next Tuesday's primary to challenge Republican representative John Katko.
Mr Sanders is also delivering a speech in Albany.