Los Angeles: With the Democratic presidential nomination effectively wrapped up, Hillary Clinton's campaign still urged supporters to vote in Tuesday's nominating contests and bring a definitive end to her protracted primary battle against Bernie Sanders.
Clinton secured enough delegates to win the nomination before Tuesday's voting, U.S.
media outlets reported on Monday night.
But Clinton campaign manager Robby Mook said they were pushing supporters and volunteers to "stay at this" for the contests in New Jersey, Montana, North Dakota, South Dakota, New Mexico and California - where she still risks a loss to Sanders.
A former U.S. secretary of state, Clinton would be the first woman presidential candidate of a major U.S. political party.
"We're on the verge of making history, and we're going to celebrate that tonight," Mook told CNN."There's a lot of people we want to make sure turn out today.
We do not want to send a message that anybody's vote doesn't count."
California is the biggest prize on Tuesday - the last and largest state to vote in what became a surprisingly tough Democratic primary race to pick a nominee for the Nov.
8 presidential election.
If Sanders, who was trailing in polls in California until recently, won the state, it could hamper Clinton's ability to unify the party ahead of its convention next month.
Clinton is anxious to turn her full attention to the general election campaign against presumptive Republican nominee Donald Trump.
"We will look forward tonight to marking having reached the threshold of a majority of the pledged delegates," Clinton spokesman Brian Fallon told CNN, referring to delegates won in primary contests."And at that point, Bernie Sanders will be out of our race."
Clinton secured the endorsement on Tuesday of Democrat Nancy Pelosi of California, who withheld her support until voting day.
President Barack Obama was eager to start campaigning, the White House said, but wanted to give voters an opportunity to cast ballots before weighing in on the Democratic race.
Despite growing pressure from party luminaries to exit the race, Sanders, a U.S.
senator from Vermont who describes himself as a democratic socialist, has vowed to continue the fight until the party convention that formally picks the nominee.
He has commanded huge crowds in parks and stadiums, galvanizing younger voters with promises to address economic inequality.
But Clinton has continued to edge him out, particularly among older voters with longer ties to the Democratic Party.
Her more pragmatic campaign has focused on building on Obama's policies.
Will Dove, 50, a startup business owner from Princeton, New Jersey, said Sanders' policy proposals were simply too ambitious and unrealistic.
Dove, speaking outside his polling place in New Jersey, where Clinton is expected to win by large margins, said Clinton was the "only practical candidate we're left with" despite her flaws and added that he would be "mortally embarrassed" if Trump prevailed in November.
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 party's July 25-28 convention are awarded by popular votes in state-by-state elections, and Clinton has a clear lead in those "pledged" delegates.
But the delegate count, where Clinton's support outnumbers Sanders' by more than 10 to 1, also includes "superdelegates" - party leaders and elected senators, members of Congress and governors - who in theory can change their mind at any time.
For that reason, the DNC has echoed the Sanders campaign, saying the superdelegates should not be counted until they actually vote at the Philadelphia convention.
In practice, superdelegates who have announced their intention are unlikely to change their minds.
The AP and NBC reported that Clinton had reached the 2,383 delegates needed to become the presumptive Democratic nominee with a decisive weekend victory in Puerto Rico, a U.S. territory, and a burst of last-minute support from superdelegates.
Clinton faces a challenge to win over Sanders supporters.
They have become increasingly resistant in recent months, with fewer than half saying they would vote for her if she becomes the party's nominee, according to a Reuters/Ipsos poll in May.
Last month, 41 per cent of Sanders supporters said they would vote for Clinton if she runs against Trump in the general election.
That was down from 50 per cent in April, and 52 percent in March.
Those who have decided not to support Clinton are split on what to do if Sanders quits the race.
Some may cross party lines and vote for Trump, but many others appear to be interested in a third-party candidate.
Some 27 per cent of Sanders supporters said in May that they would vote for neither candidate or another alternative.
The Reuters/Ipsos poll included 2,919 Sanders supporters during the month of May and has a credibility interval, a measure of accuracy, of 2 percentage points.
The prospect of a Trump presidency may influence some Sanders supporters to get behind Clinton.
Nancy Green, 70, of Princeton, New Jersey, cast her ballot of Clinton on Tuesday, despite thinking that she shares more political positions with Sanders.
"I think Hillary is not a nice person," she said."But it scares me that Donald Trump might win."