Donald Trump stepped up his attacks on Hillary Clinton Tuesday as her campaign battled to silence suggestions that donors to her family's charity paid for access when she was America's top diplomat.

The Democratic nominee, looking to make history as America's first female commander-in-chief, is polling well ahead of her Republican rival but has hit choppy waters this week as the Trump campaign has fought to rebound from a series of damaging self-inflicted wounds.

‘Hillary Clinton is totally unfit to hold public office,’ Trump told a rally in Austin, Texas interrupted several times by protesters.

‘It is impossible to figure out where the Clinton Foundation ends and the State Department begins,’ he added.

Hours earlier, the Associated Press reported that more than half the people outside government who met Clinton while she was secretary of state donated money to the Clinton Foundation.

‘It is now abundantly clear that the Clintons set up a business to profit from public office, they sold access,’ he said.

‘This is corruption and this is why I have called for a special prosecutor to look into this mess,’ he said.

The Trump campaign demanded an independent probe after conservative group Judicial Watch, which has targeted Clinton for years, released nearly 15,000 emails sent from her private server.

Among the emails are some purporting to show that donors to the Foundation lobbied one of her top aides, Huma Abedin, for access to Clinton.

Asked whether Trump's donation of tens of thousands of dollars to the Clinton Foundation was also an attempt to gain access, campaign manager Kellyanne Conway told CNN he ‘wasn't paying to play.’

‘He has never told me he was going to the State Department to have a meeting with Hillary Clinton,’ she said.

Clinton, who on Tuesday attended a Hollywood fundraiser at the home of Justin Timberlake and his wife Jessica Biel, has so far not commented publicly on the report.

But her campaign spokesman dismissed the AP analysis as based on ‘utterly flawed data’ that ‘cherry-picked’ from her schedule.

- Misrepresent -

‘The data does not account for more than half of her tenure as secretary,’ Brian Fallon said in a statement.

‘Just taking the subset of meetings arbitrarily selected by the AP, it is outrageous to misrepresent Secretary Clinton's basis for meeting with these individuals,’ he added.

The charity has raised some $2 billion since it was founded in 2001 after Bill Clinton stepped down as president and disburses funds domestically and overseas, handing out some $218 million in 2014.

Bill Clinton announced this week that if his wife is elected, the foundation will accept only US contributions, that he will step down from the board and will no longer raise funds for the charity.

With Clinton now leading 47 percent to Trump's 41.5 percent, according to an average of national polls from Real Clear Politics, it is unclear to what extent the new reports can damage her standing.

US voters remain alarmed by Trump's lack of experience, question whether he has the temperament for the job and a series of high-profile blunders have chipped away at his populist appeal.

Trump used the rest of his speech in Texas to make another sustained pitch for African-American voters -- who vote overwhelmingly Democrat -- and highlight poor border security in Texas.

He reiterated calls to build a wall on the southern US border with Mexico in a bid to stop illegal immigration, a structure he said Mexico would pay for.

He also repeated his calls for ‘extreme vetting’ of immigrants, saying ‘hundreds of immigrants and their children’ had been charged with terrorism in the United States since the September 11, 2001 attacks.

He promised to create safe zones in the Middle East, funded by Gulf States for refugees fleeing conflict and for visas to be suspended ‘when we can't perform effective screening.’

He was briefly joined on stage by mothers whose children were killed by illegal immigrants. ‘Your children did not die in vain, because we're not going to allow it to happen to others,’ he told them.