LONDON—The former Cambridge Analytica data guru who came forward to claim that the Trump political consultants had misused 50 million Facebook profiles in the 2016 presidential election has hit back at critics questioning his status as a genuine whistleblower.

Christopher Wylie said the prospect of being “crushed” by billionaire Republican backer Robert Mercer prevented him from coming forward sooner.

Since Wylie went public, Facebook shares have tanked, the CEO of Cambridge Analytica has been suspended, and U.S., British, and European authorities have launched inquiries into the use of personal data in the 2016 campaigns.

Wylie believes the data analytics and targeted online campaigns he helped to pioneer at Cambridge Analytica were intrinsic to the campaigns that upturned the political world in 2016—first through Brexit and then the election of Donald Trump.

The Daily Beast asked Wylie why he had not blown the whistle before it was too late to stop Brexit and Trump. “I didn’t fully appreciate the impact of what I helped create until 2016 happened,” he said. “Very soon after that, I started working for The Guardian, originally as an anonymous source.”

Wylie began communicating with investigative reporter Carole Cadwalladr a few months after Trump’s shock election victory. He said he went to the authorities first and then began to leak information about the work of Cambridge Analytica by the spring of 2017.

“Firstly, we should be encouraging people who know about wrongdoing—even if they were involved in it—we should be encouraging those people to come forward,” he said. “Secondly, I didn’t come forward because I got sued almost immediately after leaving [in late 2014] and I had to sign not just an NDA but an undertaking of confidence, and it was quite intimidating to go up against Robert Mercer, who’s a billionaire who threatens to crush you.”

Mercer, who was Trump’s biggest backer in the race against Hillary Clinton, is a major investor in Cambridge Analytica but has never been on its board, and a source told The Daily Beast this month that he was just a passive investor while his daughter Rebekah has a more hands-on role and a place on the board.

Wylie told The Daily Beast that it wasn’t Rebekah Mercer, whom he said he met several times, who paid close attention to the data scraping and voter targeting tools Cambridge Analytica was using. “No, that was Robert Mercer. Robert Mercer was interested in what we were doing—in terms of the actual technical processes,” he said. “Rebekah Mercer just wanted stuff to happen. She is a difficult and demanding woman to work for.”

Wylie said that after Trump’s election, which came almost two years after he had left Cambridge Analytica, the first action he took was to report himself and the company to the authorities in Britain, where he lives.

“The other thing that I did is I went and talked to other people I know to gather evidence,” he said. “That took months and months and months, and I promise you that was very difficult to do because when you talk to someone who has been intimidated over and over and over again by a billionaire and by Steve Bannon, it is hard to convince them to risk trusting someone else with information that could be incredibly compromising to them.”