“One of his minions, I believe, went back and either called him or spoke to him and said, ‘There’s nothing we can do about it, bro,‘” said the server, who would only give his name as Mike.

A man who later answered the door told a POLITICO reporter that he didn’t know anything about the subpoena or the attempted service. The townhouse was once known as the headquarters of the conservative website Breitbart News, of which Bannon served as executive chairman.

“Government agencies serve thousands of subpoenas for all types of minor and often irrelevant information. This is a non event,” Alex Spiro, an attorney representing Bannon, told POLITICO via email.

Bannon told Vanity Fair last year that Facebook is to blame for the sort of data abuses at issue in the Cambridge Analytica case: “They take your stuff for free and monetize it for huge margins." FTC spokespeople declined to answer questions about the probe.

The civil investigative demand, which POLITICO viewed, said the commission is examining whether Bannon’s "practices regarding the collection and use of consumers’ information from Facebook were deceptive or unfair," and "whether a Commission action to obtain money relief would be in the public interest.”

The subpoena is an outgrowth of the Cambridge Analytica controversy that exploded into view in March 2018, with the revelation that the company had improperly exploited a quiz app on Facebook to suck up data on tens of millions of people for voter targeting operations.

The FTC settled its case with Facebook over the scandal in July with a record-setting $5 billion fine. But the agency's probe into Cambridge Analytica continues. In July, the FTC filed a lawsuit against the firm, alleging that it deceived Facebook users by harvesting their information without their consent. That data was paired with other records to build psychological profiles used to target voters, the commission said.

The FTC issues civil investigative demand letters to individuals and entities that are either the subject of any agency investigation or are believed to have information of interest to investigators. When recipients of demand letters don't comply, the FTC's general counsel may step in to have it enforced by the courts, according to the agency.

Bannon played an early role in getting Cambridge Analytica off the ground and served on the firm's board. He saw the company, launched in 2013 and financially backed by Republican mega-donor Robert Mercer, as a way of tapping cutting-edge data science to power a global nationalist movement. A former contractor for Cambridge Analytica turned whistleblower, Christopher Wylie, told CNN in 2018 that the company was "Steve Bannon's baby."

The FTC in July reached a proposed settlement with two key figures tied to Cambridge Analytica, former CEO Alexander Nix and Aleksandr Kogan, the academic who developed the quiz app. Cambridge Analytica filed for bankruptcy in 2018.

Investigators in both the U.S. and UK have probed whether Cambridge Analytica had connections to Russian actors who used Facebook and other social media to try to manipulate the 2016 presidential election in Trump's favor. The office of Special Counsel Robert Mueller also looked into that issue as part of his investigation into Russian election interference, but no mention of the firm appears in Mueller's final report issued in April.

Trump named Bannon his chief strategist in the White House in November 2016, shortly after winning office. Bannon's rocky tenure there ended in August 2017, when he left as part of a White House shake-up led by then-chief of staff John Kelly.

