Trump campaign links with Cambridge Analytica being investigated by Robert Mueller

British political consulting firm accused of psychologically profiling people and delivering material supporting US president

Robert Mueller, the Special Counsel investigating alleged Russian interference in the US election, will scrutinise links between Donald Trump's campaign and Cambridge Analytica - the British firm accused of using the personal information of millions of Facebook users for campaigning, without their consent or knowledge.

Mr Mueller’s investigators have questioned officials who worked on the US President’s campaign about its data operations, particularly about how they collected and used voter data in battleground states, according to two sources close to the investigation.

Authorities in Britain and the US are investigating whether Cambridge Analytica may have used data improperly obtained from more than 50 million Facebook users to try to influence the 2016 White House race.

Several digital experts employed by the Republican National Committee (RNC) worked closely with both the campaign and the London-based data-mining firm, according to the two former campaign officials.

The campaign paid the firm just under $6m (£4.26m) for its work, federal records show.

Mr Mueller is leading a criminal probe into whether President Trump’s team had ties to Russia and whether he may have obstructed justice. He has subpoenaed the Trump Organization in the investigation into alleged collusion between members of the President's 2016 team and Russian officials.

The Trump campaign has distanced itself from Cambridge Analytica, which had been financed by major Republican donors and, for a time, employed Steve Bannon, the former editor of right-wing outlet Breitbart News, who later became Mr Trump’s former chief strategist.

The exact role that Cambridge Analytica played for the Trump campaign remains unclear. Staff at the firm are known to have made several overtures to campaign officials before the firm was eventually retained.

They first requested a meeting in spring 2015, before the billionaire real-estate mogul officially announced his candidacy, according to four former campaign officials.

Alexander Nix, the Cambridge Analytica chief executive, captured on a sting video released this week, met with then-campaign manager Corey Lewandowski to make a pitch about what his company could offer, including its “psychographic method” of profiling.

Mr Lewandowski refused, in part because staff believed Mr Trump would not be willing to make a sizeable financial investment in an analytics firm, according the two sources.

Cambridge Analytica then worked for the campaign of Mr Trump’s Republican rivals Ben Carson and Ted Cruz. But after Mr Trump became the presumptive nominee, the data firm again made contact, this time with Paul Manafort, the new campaign chief.

Mr Manafort was also sceptical, but hired Cambridge Analytica, in part as a friendly gesture to the Mercer family, heavyweight Republican donors who had helped fund the company’s launch a few years earlier.

Records show the Trump campaign’s first payment of $100,000 (£70,000) to the firm came in July 2016.

Five of the firm’s staff were assigned to work with the campaign’s digital director, Brad Parscale, at his Texas-based firm. Parscale and Jared Kushner, Mr Trump’s son-in-law, emphasised using social media — particularly Facebook — to better target voters, and pressed its importance on Mr Trump.

Cambridge Analytica built a database of small-dollar Republican donors, information the company had from its prior work for the Cruz and Carson campaigns.

But when it became clear the RNC would share its much-improved data operation with the Trump campaign, the firm fell out of favour. Two of the former officials said their tools were not useful, though Parscale said a month after the election that the firm had been involved in daily polls and helped shape spending.

Another campaign official said the firm was kept around mostly to placate the Mercers and their allies on Trump’s staff.

Mr Bannon, with the Mercers’ backing, served as vice president of the firm from June 2014 to August 2016, when he joined the Trump campaign. He recently tried to distance the campaign from Cambridge Analytica, saying he had no knowledge of the data-mining operation, instead blaming Facebook.

Chris Wylie, a Cambridge Analytica whistleblower, told The Washington Post that the firm had begun testing phrases such as “drain the swamp” before Mr Trump launched his campaign.

Senator Mark Warner, vice-chairman of the Senate Intelligence Committee, said the scandal was “more evidence that the online political advertising market is essentially the Wild West.”

“Whether it’s allowing Russians to purchase political ads, or extensive micro-targeting based on ill-gotten user data, it’s clear that, left unregulated, this market will continue to be prone to deception and lacking in transparency,” he tweeted.

AP contributed to this report.