Almost eight years to the day after ending her first presidential bid while celebrating the 18 million cracks her supporters put in the “highest, hardest glass ceiling,” Hillary Clinton took a major step towards breaking through that final barrier Monday evening, and towards becoming the country’s first woman president.

Close video Clinton as presumptive nominee, how the projection was made John Lapinski, director of elections for NBC News, talks with Rachel Maddow about the calculations that go into the determination that a candidate, in this case Hillary Clinton, is the project presumptive nominee of a party. John Lapinski, director of elections for NBC News, talks with Rachel Maddow about the calculations that go into the determination that a candidate, in this case Hillary Clinton, is the project presumptive nominee of a party. share tweet email Embed

The projection, based on new commitments from superdelegates, came one day before voters in California and five other states were set to push Clinton over the threshold of delegates needed to claim the party’s presumptive nomination.

“It’s been an incredible journey,” Clinton told reporters Monday in California before she was declared the presumptive nominee. “My supporters are passionate. They are committed. They have voted for me in great numbers across our country for many reasons. But among those reasons is their belief that having a woman president will make a great statement, a historic statement, about what kind of country we are, what we stand for. It’s really emotional.”

The historic nature of Clinton’s candidacy has been an undercurrent throughout her second presidential bid, but rarely at its forefront. That will likely change Tuesday night when Clinton declares victory at a celebratory rally with supporters in Brooklyn.

“It’s a revolution, really,” said Terry O’Neill, the president of the National Organization for Women. “It’s not quite yet the highest, hardest glass ceiling, because that would be the presidency, but it’s just an amazing first.”

RELATED: Clinton hits ‘magic number’ of delegates to clinch nomination

Rival Bernie Sanders was defiant Monday evening as major news outlets declared Clinton the presumptive nominee, saying he would stay in the race and keep fighting until the party’s convention in July.

Sanders spokesperson Michael Briggs blasted the media’s “rush to judgement,” and stated that “Clinton does not have and will not have the requisite number of pledged delegates to secure the nomination.”

The Vermont senator’s campaign has insisted that superdelegates should not be counted until they vote at the Democratic National Convention. However, news outlets have historically projected winners based on public commitments from the party leaders, who very rarely change their minds after making a public declaration.

Sanders has put all his hopes on Tuesday’s primary in California, where he’s pulled even with Clinton. Losing California would be seen as an embarrassment for the newly minted presumptive nominee, and dampen her historic day. At the same time, it would embolden Sanders to take his challenge as far as possible.

But the outcome of the nominating contest is no longer in doubt.

RELATED: Sanders blames media’s ‘rush to judgement’ as Clinton hits delegate majority

On top of her overwhelming lead among superdelegates, Clinton is on track to claim a majority of pledged delegates after Tuesday’s contests. The former secretary of state came out of her weekend wins in Puerto Rico and the Virgin Islands close enough to reaching the pledged delegate threshold that she needs only to add one of every three delegates available in Tuesday’s contests to do so.

If Clinton gets the pledged delegate majority, Sanders’ only hope will be to convince a large list of superdelegates to override the will of the voters and make him the nominee.

“This is an important milestone,” Clinton campaign manager Robby Mook said in a statement Monday after news outlets called the race. “[B]ut there are six states that are voting Tuesday, with millions of people heading to the polls, and Hillary Clinton is working to earn every vote. We look forward to Tuesday night, when Hillary Clinton will clinch not only a win in the popular vote, but also the majority of pledged delegates.”

Still, for activists who have been eager to see a woman become president, getting as close as Clinton has is exhilarating.

Close video Despite projection, Clinton still planning to work for every vote Robby Mook, Clinton campaign manager, talks with Rachel Maddow about Hillary Clinton’s determination to continue competing for the Democratic nomination to make the math official, and how the Clinton campaign hopes to come together with Sanders… Robby Mook, Clinton campaign manager, talks with Rachel Maddow about Hillary Clinton’s determination to continue competing for the Democratic nomination to make the math official, and how the Clinton campaign hopes to come together with Sanders… share tweet email Embed

Stephanie Schriock, president of Emily’s List, the deep-pocketed group that helps elect female Democrats, noted that it’s been almost exactly 100 years since the first woman was elected to Congress in 1917 – Jeannette Rankin from Montana. More than 300 women have been elected since, and Clinton and her supporters are building on their work, Schriock said.

“If it was easy, it would have happened long ago,” Schriock said. “Things are getting easier, but a lot of groundwork needed to be laid. A lot of elections needed to be won.”

Women are still dramatically underrepresented in the Congress and statehouses across the country, and advocates hope that Clinton’s ascension will help close that gap.

“If you can’t see it, you can’t be it,” said Teresa Younger, the president of the Ms. Foundation for Women. “That young women and men will get the chance to see a woman running as a major party candidate is really important.”

RELATED: Report: President Obama is ready to endorse Hillary Clinton

In 2008, Clinton downplayed her gender and got beat by a candidate who went on to be first African-American president. Her advisers feared the country was not ready for a woman president, and even less so for a feminist one. This year, she seemed more comfortable leaning into into the idea of making history.

“It’s obvious that sexism stopped a woman from being president for nearly 200 years of American history, and once women came into the political arena, it wasn’t exactly like the old boy’s club was rolling out the red carpet,” said Nancy L. Cohen, the author of book “Breakthrough: The Making of America’s First Woman President,” which came out earlier this year.

But Cohen thinks Clinton has an opportunity in the general election against a “certifiable misogynist” like Donald Trump. “Sometimes I think Trump’s real slogan is make America manly again,” Cohen said. “I think that Clinton has showed that she likes to fight those kind of bullies, and she feels like she’s fighting for all women. I think her best self as a campaigner comes out in these situations.”

Clinton will still have to contend with Sanders, who responded sharply to a question Monday about whether it was sexist for him to stay in the race and potentially endanger the election of the first woman president.

RELATED: Gender and the presidency: A look through polling history

“Is that a serious question?” Sanders snapped. “To say that it is sexist that any – so if Hillary Clinton runs for president is your point – that it is sexist for any man to oppose her?”

There’s plenty of work ahead for Clinton, primarily integrating Sanders and his supporters into the party ahead of the contest with Trump.

“I hope everybody takes a moment to be really excited,” said Schriock. “And then we gotta role up our sleeves and get ready for November.”

For the women’s movement as a whole, the struggle does not end at the White House.

“My concern is always that people think we will have reached full equality if we have a woman running as a major party candidate,” said Younger. ”We did not become a post-racist society after President Obama was elected. We will not become a post-feminist society if Hillary Clinton is elected.”