NEW YORK, United States (AFP) — Hillary Clinton was looking ahead Wednesday to a general election showdown against Donald Trump, hours after making history by clinching the Democratic Party nomination.

“Thanks to you, we’ve reached a milestone,” a beaming Clinton told ecstatic supporters in New York, “the first time in our nation’s history that a woman will be a major party’s nominee.”

The former secretary of state took a dramatic step toward the White House by winning primaries in California, New Jersey, New Mexico and South Dakota, four of six states holding polls on the last major date of the 2016 primary calendar.

California, the most populous US state, was the biggest prize of all.

Newspapers marked Clinton’s achievement on their front pages Wednesday, including the New York Post tabloid which ran the headline “The First Lady” – a nod to her previous White House role.

The primary victories effectively put an end to Clinton’s battle with challenger Bernie Sanders, the self-declared democratic socialist senator from Vermont who waged an extraordinarily successful grassroots campaign.

But Sanders, ignoring the political writing on the wall, vowed to “continue the fight.”

“Our mission is more than just defeating Donald Trump, it is transforming our country,” he declared to supporters in Santa Monica, California.

Clinton, 68, is now headed toward a colossal showdown in November with Trump, the bombastic Republican flagbearer.

“We believe that we are stronger together and the stakes in this election are high, and the choice is clear,” she said, before launching into a frontal attack on her Republican rival.

“Donald Trump is temperamentally unfit to be president and commander in chief,” she said, using rhetoric that would have been unthinkable before this tempestuous election season.

Clinton held a commanding lead over Sanders even before Tuesday’s votes, having passed the magic number of 2,383 delegates required to clinch the nomination.

She must now reconcile a bruised and deeply divided party and rally it behind her in the brutal match against Trump.

Sanders has harnessed a tidal wave of anger at the ruling political class.

With an insurgent campaign he challenged Clinton harder for the party nomination than most believed was possible.

The drive for party unity is likely to receive a shot in the arm when Obama comes off the sidelines and offers his endorsement of Clinton, as soon as Wednesday.

That will not come as a surprise, but it could serve to coax hardline “Bernie or bust” fans back into the party tent.

Obama has approval ratings above 80 percent with liberal democrats who make up the bulk of Sanders’ support.

The White House announced that Obama telephoned both candidates to congratulate them on their hard-fought primary race, and said the president would meet with Sanders on Thursday, “at Sanders’ request,” at the White House.

Trump, who himself crossed the Republican threshold Tuesday although it was a foregone conclusion, signaled he plans to go on the offensive against Hillary and Bill Clinton.

“The Clintons have turned the politics of personal enrichment into an art form for themselves,” he told supporters at his golf property in New York state.

Trump said he will deliver a “a major speech” early next week when he will be “discussing all of the things that have taken place with the Clintons.”

“I think you’re going to find it very informative and very very interesting.”

Clinton remains mired in scandal about her use of a private email server as secretary of state and perceptions of dishonesty – leaving her with unpopularity ratings surpassed only by the controversial Trump.

The billionaire has faltered badly since he won the Republican nomination, with violence-marred rallies, run-ins with the press and a widely condemned attack on a Mexican-American federal judge who is investigating his now-defunct Trump University.

Leaders of Trump’s own Republican Party, including House Speaker Paul Ryan, described that as textbook racism.