United States presidential candidates Hillary Clinton and Donald Trump have kicked off a fierce general election battle.
United States presidential nominees Hillary Clinton and Donald Trump. Photo: AFP
Democrats have accused Mr Trump of erratic behavior, while the Republican is threatening to bring up old Clinton scandals.
A former secretary of state, Mrs Clinton made history when she became the first woman to be nominated by one of the major political parties for the presidency.
Primary election wins on Tuesday in California and elsewhere catapulted her to victory over Democratic opponent Bernie Sanders.
If elected on 8 November, the 68-year-old would return the Clinton family to the White House 16 years after her husband Bill Clinton's second term ended in impeachment.
All signs point toward a negative campaign for five months, with Mrs Clinton accusing Mr Trump of being temperamentally unfit to serve, and the New York billionaire saying Mrs Clinton had 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 critical comments from Republicans themselves to portray 69-year-old Mr Trump as unfit for the Oval Office after he repeatedly accused Mexican-American judge Gonzalo Curiel of bias against him because of his ancestry.
"The most effective thing to do with Donald Trump is just to get his words out there and let him speak for himself," Mrs Clinton's campaign manager Robby Mook told CNN on Wednesday.
Mr Mook charged Mr Trump with a history of "erratic behavior", the same language leveled by the Obama campaign in its defeat of Republican nominee John McCain in 2008.
Democratic presidential candidate Hillary Clinton arrives onstage to deliver her victory speech. Photo: AFP
Mr Trump meanwhile gave a carefully crafted primary race 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.
Mr Trump said money given to the Clinton Foundation charity from foreign donors had 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.
"Hillary Clinton turned the State Department into her private hedge fund - the Russians, the Saudis, the Chinese - all gave money to Bill and Hillary and got favorable treatment in return," he said.
"It's a sad day in America when foreign governments with deep pockets have more influence in our own country than our great citizens."
He said he would give a speech the following week "discussing all of the things that have taken place with the Clintons".
A lead for Mrs Clinton
A Reuters/Ipsos poll released on Tuesday showed Mrs Clinton leading Mr Trump by 10 percentage points nationally, little changed from a week earlier.
Both candidates have work to do to unite their parties behind them but the Democrat appeared to face the easier path, with leftist Vermont Senator Mr Sanders nearly out of options to challenge her.
Mr Trump faced an uphill battle with many party leaders still opposed to him.
US House of Representatives Speaker Paul Ryan described Mr Trump's remarks about Dr Curiel as a "textbook definition of a racist comment" but said he would still support him.
Mr Ryan met behind closed doors on Wednesday with House Republicans. An aide said he "discussed with his members the thinking behind his endorsement and how to move forward," and reiterated he had confidence Mr Trump would support the House Republican agenda.
Republicans complained that Mr Trump still engaged in petty battles with former rivals and was behind in building a fund-raising organisation.
Mr Trump was to meet on Thursday in New York with top fundraisers of the Republican National Committee, a party official said.
"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," US 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.
Speaker of the House Paul Ryan. Photo: AFP
Democrats close ranks
Mrs Clinton edged Mr 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 fellow Democrat Mr Obama.
Democratic Party elites were lined up squarely behind Mrs Clinton, including most likely Mr Obama, who may endorse her as early as this week.
Pressure would mount for Mr Sanders to exit graciously and throw his support to Mrs Clinton.
Mr Obama congratulated Mrs Clinton on her nomination win in a phone call and will meet Sanders on Thursday at the senator's request.
The Associated Press called the race in California for Mrs Clinton early on Wednesday. She won 56 percent to Mr Sanders' 43, 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. Mr Sanders won in Montana and North Dakota.