The joint appearance at a high school in Portsmouth, New Hampshire — their first — was the culmination of weeks of talks between the two campaigns aimed at unifying the party to most effectively take on Republican Donald Trump in November.

“Secretary Clinton has won the Democratic nominating process, and I congratulate her for that,” Sanders, 74, told a cheering crowd, with Clinton at his side.

“She will be the Democratic nominee for president and I intend to do everything I can to make certain she will be the next president of the United States.”

The US senator from Vermont offered voters a litany of reasons why the 68-year-old former secretary of state is a better choice than the 70-year-old Manhattan real estate mogul.

“If anyone out there thinks that this election is not important, take a moment to think about the Supreme Court justices that Donald Trump will nominate, and what that means to civil liberties, equal rights and the future of our country,” Sanders said.

Putting aside the acrimony, Clinton thanked Sanders for his endorsement — even if their body language did not exude warmth and was downright awkward at times.

“I am proud to be fighting alongside you,” she said. “We are stronger together.”

– ‘Most progressive platform’ -Sanders waged a tougher-than-expected, year-long battle against Clinton, but in early June she clinched enough delegates to secure the nomination.

The feisty self-described democratic socialist nevertheless had refused to concede defeat to his more moderate rival, although recently he said he would vote for Clinton.

Sanders wants to ensure that his ideas are part of the party platform presented at the Democratic National Convention later this month in Philadelphia, when Clinton is formally nominated.

Sanders said that at weekend talks in Orlando, “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.”

The party reached agreement on language concerning climate change, health care and raising the US minimum wage to $15 per hour. They reportedly failed to reach common ground on the Trans-Pacific Partnership trade accord.

– Trump mulls running mate -Trump, who has proclaimed himself “the law and order candidate” amid rising gun violence, unleashed a barrage of criticism, saying Sanders “abandoned” his grassroots supporters by joining forces with Clinton.

But he made another appeal to Democrats and independents who had backed Sanders.

“To all the Bernie voters who want to stop bad trade deals & global special interests, we welcome you with open arms,” Trump wrote.

The Republican billionaire will campaign later Tuesday in Indiana, where his scheduled appearance with Governor Mike Pence was raising speculation that he could pick the state’s chief executive as running mate.

Trump told The New York Times he expected to make an announcement by Friday, three days before the Republican convention in Cleveland where Trump will officially become the nominee.

“I have five candidates, plus two, two that are unknown to anybody,” Trump told the daily in a phone interview.

Trump hit the campaign trail Monday in Virginia Beach with New Jersey Governor Chris Christie — one of those on the vice presidential shortlist.

Christie’s experience running a populous state could be seen as critical for Trump, who has acknowledged his own lack of political and government expertise.

Indiana’s Pence also brings executive experience, and the salt-of-the-earth Midwesterner has shown a steady hand that could help counter the narrative that Trump is too incendiary and quick to provoke.

He is a 12-year veteran of Congress, well versed in international affairs from his time on the House Foreign Affairs Committee.

And he could serve as a bridge to Capitol Hill, having joined the House at the same time as Paul Ryan, the current speaker.

Pence made a tepid endorsement of Ted Cruz, a conservative senator from Texas, but switched to Trump when Cruz dropped out.

In the Times interview, Trump called Christie “strong” and Pence “solid as a rock.”

Former House speaker Newt Gingrich is also in the running mate mix. Asked about Gingrich, who ran unsuccessfully for president in 2012, Trump told the paper, “Newt is Newt. He’s a good guy.”

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