The company is also under investigation by British officials for its use of Facebook users’ data.
Sources tell ABC News several digital experts who worked in support of Trump’s bid in 2016 have met with Mueller's team for closed-door interviews. The staffers, most of whom were employed by the RNC, served as key members of the 2016 operation working closely with the campaign and the data firm, the sources said. The company worked closely with the Republican candidate’s political team.
The Trump campaign declined to comment and the Republican National Committee has not responded to ABC News' request for comment.
Cambridge Analytica was brought on by then-Trump campaign digital advisor Brad Parscale in early June 2016, after the data science firm pitched him on its services, sources told ABC News. Three Cambridge Analytica employees, including two data scientists, immediately moved to San Antonio to embed with Parscale's firm and by August, the number of fulltime staffers in Texas ballooned to 13.
Parscale would eventually leave Texas to move into Trump Tower in September, and the data firm sent a mid-level employee with him to interpret daily polling reports, according to sources.
Cambridge Analytica was one entity involved in creating the voter information and fundraising database now known as Project Alamo, built jointly by staffers from the RNC, the Trump campaign and Parscale's firm with data supplied by the RNC and the campaign, sources said.
A spokesperson for the Trump campaign told ABC News in a statement that they “used the RNC for its voter data and not Cambridge Analytica. Using the RNC data was one of the best choices the campaign made. Any claims that voter data were used from another source to support the victory in 2016 are false.”
A source with direct knowledge who has met with the special counsel's team tells ABC News investigators have asked former senior level campaign staff about the digital operations, specifically how data was collected and used and how assets were targeted specifically in the battleground states. Mueller's team has asked witnesses about the process of "micro targeting" which is the process of using data to identify specific groups of individuals and thereby influence their thoughts and potentially their actions.
From the start, Trump and his top advisors have touted the campaign’s mastery of spinning pithy social media messages into votes.
"I understand social media. I understand Twitter, I understand the power of Twitter I understand the power of Facebook. Maybe better than almost anybody, based on my results," Trump said at a 2015 town hall in South Carolina.
“We found that Facebook and digital targeting were the most effective ways to reach the audiences. After the primary, we started ramping up because we knew that doing a national campaign is different than doing a primary campaign," Kushner told Forbes Magazine just after the election. "That was when we formalized the system because we had to ramp up for digital fundraising. We brought in Cambridge Analytica.”
In an undercover video aired on the British television Channel 4, the managing director of Cambridge Analytica's political division, Mark Turnbull, appears to describe, the effort to a reporter posing as a potential client.
Turnbull said his firm created memes around the “Crooked Hillary” brand, not necessarily the name itself.
“The brand was ‘Defeat crooked Hillary,’” he said. “Sometimes you could use proxy organizations… charities, or activist group. We feed them the material and they do the work. We just put the information into the bloodstream on the internet and then watch it grow. Give it a little push every once in a while. .. it’s un-attributable. Untraceable.”
Cambridge Analytica in a statement said it deleted all the Facebook data and related information in cooperation with the social media company, and that such information was never used as part of the data firm's work with the Trump presidential campaign. The data firm has said it was unaware the data was improperly obtained by a third party and that is was destroyed as soon as they were made aware.
Aleksandr Kogan, the psychology researcher at Cambridge University, who developed the app to collect the data from Facebook users that Cambridge Analytica used told the BBC that he is “being basically used as a scapegoat” by the social media company and data firm.
"Honestly, we thought we were acting perfectly appropriately, we thought we were doing something that was really normal," he told the news outlet.
The Trump campaign has said they never used data from Cambridge Analytica.
On Tuesday, the data firm announced CEO Alexander Nix’s suspension, pending an investigation and the release of several undercover videos, aired by Channel 4, of him bragging about Cambridge Analytica’s use of sex workers and bribes to damage politicians for their clients.
In the video, Nix is also recorded as saying the company used a method of communicating with clients that ensure emails “disappear” after they have been read.
“You send them and after they’ve been read, two hours later, they disappear,” Nix said in the undercover Channel 4 News video. “There’s no evidence, there’s no paper trail, there’s nothing.”
ABC News has not verified Nix’s on camera claims in the Channel 4 reports.
The data firm has been under fire this week after reports that the company used data harvested from millions of Facebook users without consent beginning in 2014 through an app. The company claims the material was obtained by a third party and has denied wrongdoing.
“This Facebook data was not used by Cambridge Analytica as part of the services it provided to the Donald Trump presidential campaign; personality targeted advertising was not carried out for this client either. The company has made this clear since 2016,” the company said in a statement.
Lawmakers involved in congressional investigations into Russian election interference have renewed interest in Facebook, calling for top company leaders to testify on Capitol Hill and more scrutiny of safeguards meant to protect user data.
“I think it’s time for the CEO, Mr. [Mark] Zuckerberg, and other top officials to come and testify and not tell part of the story, but tell the whole story of their involvement -- not only with the Trump campaign but their ability to have their platform misused by the Russians,” Sen. Mark Warner, D-Va., the top Democrat on the Senate Intelligence Committee, told ABC News.
Democrats on the House Intelligence Committee may soon have the opportunity to question the former Cambridge employee who helped expose the company's use of millions of Facebook profiles without their knowledge to help its political messaging efforts during the 2016 presidential election.
Christopher Wylie, the former employee, told ABC News “one of the reasons why I’m speaking out is because I think that it’s really concerning that no one has really investigated Cambridge Analytica and its role in the 2016 election.”
Wylie confirmed to ABC News that he has accepted an invitation to appear for an interview with congressional investigators.