Washington: Hillary Clinton and Republican rival Donald Trump kicked off what is shaping up to be a bitter five-month general election battle after the Democrat became the first woman to lead a major political party in its quest to capture the U.S. presidency.
Big wins for Clinton on Tuesday in California and elsewhere catapulted her to victory in the Democratic primary race over opponent Bernie Sanders.
If elected on November 8, the 68-year-old Clinton would return the Clinton family to the White House 16 years after her husband, Bill Clinton, completed two terms as president.
All signs point toward a negative campaign as Clinton accuses Trump of being temperamentally unfit to serve and the New York billionaire charges Clinton has a dark past with shades of corruption and a weak record as President Barack Obama's first-term secretary of state.
The Clinton campaign drew on comments from Trump's fellow Republicans to portray the 69-year-old Trump as not fit for the Oval Office after the real estate developer repeatedly accused a Mexican-American judge of showing bias against him because of his ethnic heritage.
"The most effective thing to do with Donald Trump is just to get his words out there and let him speak for himself," Clinton campaign manager Robby Mook told CNN on Wednesday.
Mook charged Trump with a history of "erratic behaviour," the same language leveled by the Obama campaign in its defeat of Republican nominee John McCain in 2008.
Trump, smarting from days of criticism from fellow Republicans fed up with his attacks on US District Judge Gonzalo Curiel, gave a carefully crafted victory speech on Tuesday night laying out his plan of attack.
To keep him from straying off message, he used a TelePrompter and avoided his typical stream-of-consciousness delivery.
Trump said the money flowing into the Clinton Foundation charity from foreign donors has earned the Clintons millions of dollars and had a corrupting influence when Hillary Clinton was secretary of state and used a private email server to conduct official business.
A Reuters/Ipsos poll released on Tuesday showed Clinton leading Trump by 10 percentage points nationally as they launch their general election battle, little changed from a week earlier.
Both Clinton and Trump have work to do to unite their parties behind them but the Democrat appeared to face the easier path with Sanders, a leftist US senator from Vermont, nearly out of options to challenge her.
Trump has an uphill battle, with many party leaders still opposed to him.
U.S. House of Representatives Speaker Paul Ryan on Tuesday described Trump's comments about the judge as "racism" but said he would still support him.
Republicans complain that Trump still engages in petty battles with former rivals and is way behind in building a fund-raising organization.
"We like parts of Donald Trump's message but he does need to act more presidential and he does need to transition to a general election approach," U.S.
Senator Susan Collins, a Maine Republican, told CNN.
"He is the one who keeps bringing up grievances against those who ran against him.
He needs to unite the party and he needs to unite the country," she said.
Clinton edged Sanders out in a rough-and-tumble battle that stretched over four months and 50 states.
She won support, especially among older voters, with a more pragmatic campaign focused on building on the policies of her fellow Democrat, Obama.
The president called both Clinton and Sanders on Tuesday.
The White House said he congratulated her on securing the delegates necessary to clinch the nomination and would meet Sanders on Thursday at Sanders' request.
The Associated Press called the race in California for Clinton early on Wednesday.
Clinton won 56 per cent to Sanders' 43 per cent, avoiding what would have been an embarrassing loss for her in America's most populous state.
The California win came on the heels of a decisive win in New Jersey and narrower victories in New Mexico and South Dakota in Tuesday's nominating contests.
Sanders won Montana and North Dakota.