Hillary Clinton is Presumptive Democratic Nominee for President: AP

Hillary Clinton has been declared the Democratic Party's presumptive nominee for president, just one day before six states head to the polls, including two weighty races in California and New Jersey.

The Associated Press made the projection Monday night based on the number of pledged delegates Clinton has won in primaries and caucuses, and a survey of superdelegates, who can technically still change their preference. Clinton's opponent, Bernie Sanders has said that he plans to go after superdelegates who have thrown their support behind Clinton.

"According to the news, we are on the brink of a historic, unprecedented moment," Clinton said, speaking to a crowd at Long Beach City College in Long Beach, California. "But we still have work to do, don't we?

"We have six elections tomorrow and we're going to fight hard for every single vote, especially right here in California."

Soon after the AP's projection, NBC News came to the same conclusion, projecting Clinton to be the presumptive Democratic nominee.

In a statement, the Sanders campaign said it was unfortunate that the media are ignoring the DNC's clear statement that it is wrong to count the votes of superdelegates before they actually vote at the convention in July. The campaign has stressed before that Clinton will not have the required number of pledged delegates to win the nomination by June 7 and the nomination will be decided by superdelegates at the convention.

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Speaking to NBC News after Clinton was declared the presumptive nominee, Sanders campaign spokesman Michael Briggs said that between now and the convention, they would be making a case to the superdelegates about which candidate has the best chance of defeating Donald Trump, Republicans' presumptive nominee.

Clinton was declared the presumptive nominee a day before two major primaries in California and New Jersey. That designation could influence voter turnout on Tuesday.

In particular, the projection could pose a challenge for Clinton in California, where some polls predict a tight race.

Clinton's campaign is not overplaying the projection, stressing that there are six states voting Tuesday and 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," a statement from the campaign said.

If she wins the nomination, Clinton will be the first woman to be nominated to run for president by a major party.

Image Credit: Alexander Nguyen for Patch.com

Allison Bauter contributed to this report