Hillary Clinton beat rival Bernie Sanders in New Jersey's nominating contest, expanding her lead. (Reuters Photo)

Highlights She's the first woman to lead a major party in a race for the White House

Ms Clinton will now have to win over Bernie Sanders supporters

He's vowed to stay in the race until the party formally picks its nominee

Wish Mom could have been here to see tonight. pic.twitter.com/NalmZoKoV7 — Hillary Clinton (@HillaryClinton) June 8, 2016

To every little girl who dreams big: Yes, you can be anything you want-even president. Tonight is for you. -H pic.twitter.com/jq7fKlfwGV — Hillary Clinton (@HillaryClinton) June 8, 2016

© Thomson Reuters 2016

Hillary Clinton declared herself the Democratic Party nominee for US president on Tuesday, saying she had made history as the first woman to lead a major party in a race for the White House.The former first lady, senator and US secretary of state beat rival Bernie Sanders in New Jersey's nominating contest, expanding her lead a day after she captured the number of delegates needed to clinch the nomination."Together, we secured the Democratic nomination . For the first time ever, a woman will be a major party's nominee to become President of the United States," Clinton, 68, wrote in a fundraising email to supporters.Missing her mother, shortly after her announcement, she tweeted:New Jersey was one of six states holding contests on Tuesday, including California, the big prize where Clinton was still at risk of an embarrassing loss to Sanders as she heads into a campaign against presumptive Republican nominee Donald Trump in the Nov. 8 election.Sanders, 74, was projected to win in North Dakota, and there were no immediate projections in Montana, New Mexico or South Dakota in the final series of big presidential nominating battles that began on Feb. 1 in Iowa. The District of Columbia, the last to vote, holds a Democratic primary next Tuesday.In the fundraising email to supporters, Clinton declared her campaign had broken "one of the highest, hardest glass ceilings."For her supporters, she tweeted:Clinton's race against Trump, 69, will unfold as she faces an ongoing investigation of her use of a personal email server while secretary of state. Opinion polls show the controversy has hurt Clinton's ratings on honesty and trustworthiness.Clinton, who now must try to unify the party and win over Sanders supporters, was expected to highlight the historic nature of her nomination at an event in Brooklyn on Tuesday night. Her campaign has compiled a video tying her to women's rights movements in American history.She wants to move beyond the primary battle and turn her attention to Trump. But Sanders, a democratic socialist US senator from Vermont, has vowed to stay in until July's party convention that formally picks the nominee, defying growing pressure from party leaders to exit the race.Although Sanders will be unable to catch Clinton even if he wins the primary in California, America's most populous state, a triumph there could fuel his continued presence in the race and underscore Clinton's weaknesses as she heads into the fight with Trump.Polls in California were due to close at 11 pm ET (0300 GMT on Wednesday).Sanders has commanded huge crowds, galvanizing younger voters with promises to address economic inequality. Clinton has edged him out, particularly among older voters, with a more pragmatic campaign focused on building on President Barack Obama's policies.Steven Acosta, a 47-year-old teacher living in Los Angeles, voted for Clinton on Tuesday, saying that was partly because he believed she stood a better chance of winning in November. For supporters like him, and many others, Clinton said:"I like what Bernie Sanders says and I agree with almost everything that he says," Acosta said. "The problem is that I think Republicans would really unify ... even more against him."Sanders was determined to stay in the race, even after the Associated Press and NBC reported on Monday night that Clinton had clinched the number of delegates needed to win the nomination. A Sanders campaign spokesman castigated what he said was the media's "rush to judgment."Under Democratic National Committee rules, most delegates to the July 25-28 convention in Philadelphia are awarded by popular votes in state-by-state elections, and Clinton has a clear lead in those pledged delegates.But the delegate count also includes superdelegates, party leaders who can change their minds at any time. Clinton's superdelegate support outnumbers Sanders' by more than 10 to 1.The Sanders' campaign has said it can still persuade superdelegates to switch to him, although in practice superdelegates who have announced their intentions are unlikely to change their minds.Sanders would have to get more than 60 percent of the superdelegates backing Clinton to switch their votes. So far, his campaign manager, Jeff Weaver, acknowledged they had yet to convert a single delegate.Trump, who became his party's presumptive nominee last month, outlasting 16 Republican challengers, is struggling to get the party's leaders solidly behind him after a bitter primary campaign during which he made a series of controversial statements directed at Muslims, Latinos, women and the disabled.On Tuesday night he addressed a crowd of supporters in New York, welcoming Sanders supporters "with open arms" should they decide to support him and declaring a new phase of the campaign had begun."Tonight we close one chapter in history and we begin another," Trump said.He said he planned to deliver a speech next week about Clinton and her husband, former President Bill Clinton.