PORTSMOUTH, N.H. (AP) -- Bernie Sanders, whose calls for a "political revolution" energized millions of voters across the nation, offered a long-awaited endorsement of his Democratic rival Hillary Clinton Tuesday, calling for unity just two weeks shy of the Democratic National Convention.

Standing alongside one another at an event in Portsmouth, N.H., Sanders, a self-described democratic socialist, congratulated Clinton for winning the nomination and vowed to do everything he can to help her beat presumptive Republican nominee Donald Trump.

"It is no secret that Hillary Clinton and I disagree on a number of issues - that's what this campaign has been about," Sanders said.

"There was a significant coming together between the two campaigns and we produced, by far, the most progressive platform in the history of the Democratic Party," he added. "Our job now is to see that platform implemented by a Democratic Senate, a Democratic House and a Hillary Clinton president - and I am going to do everything I can to make that happen."

Democrats have coalesced around Clinton's candidacy since she defeated Sanders in primaries last month in California and five other states, led by endorsements from President Barack Obama, Vice President Joe Biden and others.

Sanders has spent the past month seeking to influence the party's platform at the Philadelphia convention and promote electoral reforms including allowing independents to participate in future primaries. The platform includes many of his proposals, including a $15 an hour minimum wage, tougher restrictions on Wall Street and an end to the death penalty.

The event at a Portsmouth high school sought to project Democratic unity before Republicans formally nominate Trump next week in Cleveland but some Sanders' supporters in the crowd did not appear to be ready to move on.