THEY all looked so friendly, back then.

A brief video-clip posted last week by Michael Moore, the provocative US film-maker and activist, shows him appearing on Roseanne Barr's TV talk-show in November 1998, seated next to her other guest, a brash real-estate tycoon by the name of Donald Trump.

Moore was publicising his first documentary, Roger and Me, in which he had pursued Roger B. Smith, chairman of General Motors, to ask about the devastating impact of the closure of GM factories in Flint, Michigan,

“It’s terrific, I tell you, I love what he did,” Trump says of Moore and the film. “If I was Roger, I wouldn’t have liked it but I enjoyed it. I hope [Moore] never does one on me, though.” Moore and Barr both laugh.

Moore has now posted that video with an ominous message. "I know Roseanne. And I know Trump. And they are about to rue the day they ever knew me." A separate message on michaelmoore.com says: "I have been working on a secret project for the last few months" and inviting people to sign for updates and find out how they can help.

The last week, of course, has been a rough, if purely self-inflicted, one for Barr. She had been riding on waves of renewed mass popularity with the revival of her blue-collar sitcom, Roseanne, but brought all of that to an end with a spectacularly ill-judged and racist tweet. In the now-deleted message she compared Valerie Jarrett, a black former Obama administration adviser, to an ape, writing that if the Islamist political movement “muslim brotherhood & planet of the apes had a baby = vj.”

The tweet prompted the Walt Disney Co-owned network ABC to cancel the show and led to a firestorm of outraged complaints - but, given America's toxic culture wars, it was not a surprise that many on the right defended Barr and furiously attacked liberals and the media.

Barr apologized for the "bad joke" about Jarrett's "politics and her looks". She also said: “It was 2 in the morning and I was ambien tweeting,” referring to the sleeping drug - but Ambien's makers, Sanofi US, tweeted caustically that "racism is not a known side-effect of any Sanofi medication."

Trump himself suggested that Bob Iger, a top ABC executive who was behind the show's cancellation, was biased. Now Moore's unexpected intervention - specifically the warning that Trump and Roseanne "are about to rue the day they ever knew me" - has stirred interest and created headlines.

READ MORE: Roseanne Barr ‘examining options’ as she weighs up fightback

Last year Moore said he was planning a Trump documentary, called Fahrenheit 11/9. The New York Post's famed Page Six reported this week that the mooted film, for the Weinstein Company, was scrapped in the aftermath of the Harvey Weinstein scandal. "Sources say they are unsure," it added, "whether this is the same doc, which the filmmaker hopes to revive at a new studio, or a completely different pic with a similar focus."

Trump has engaged Moore's attentions before now, in the film-maker's 2016 film of his one-man show, Michael Moore in TrumpLand, and his Broadway show, The Terms of My Surrender. The mission of the former film, shot in the run-up to the 2016 election, was to “Make America Sane Again.”

Michigan-born Moore, who is 64, reportedly became America's youngest public official at 18, in 1972, when he won a seat on his school's board.

He made his reputation with such films as Roger & Me and 2002's Bowling for Columbine, about America's gun culture, prompted by the massacre at Columbine High School, Colorado, in April 1999, in which students Eric Harris and Dylan Klebold killed 12 students and one teacher before killing themselves.

The film won Moore the 2003 Oscar for Documentary Feature but he was roundly booed when he used his acceptance speech to attack President George W Bush and the invasion of Iraq. Bowling for Columbine had by then been voted the greatest non-fiction film of all time by the international documentary association.

In 2004 Moore brought out Fahrenheit 9/11, an openly partisan look at the Bush presidency, the War on Terror and the role of the media. It was greeted with wild enthusiasm at the Cannes film festival, with Weinstein, whose Miramax Films funded the project, saying it received "the longest standing ovation I've seen in over 25 years." It went on to make in excess of $119 million at the US box office.

In 2005 TIME magazine included Moore in its list of the 100 most influential people. It said: "Through endless appearances on talk shows and cable news networks, Moore never backed down from his impossible level of righteousness ... By doing so, Moore ... inspired his fellow Democrats with a workingman's toughness they have lacked for some time."

Moore's subsequent films have included Sicko, an expose of what he labelled as "the crazy and sometimes cruel" US healthcare system, and 2015's Where to Invade Next. He has also made TV films and written several books.

READ MORE: Roseanne Barr ‘examining options’ as she weighs up fightback

Moore's combative and idiosyncratic style has long generated a backlash from conservative and other opponents. In 2005 Glenn Beck, then a conservative radio host, publicly mused about "choking the life out of him." Others have assailed his lavish lifestyle and alleged that his films are laden with distortions and untruths.

Not that Moore cares too much about that. It will be interesting to see just what shape his new project, on Trump and Roseanne, will take.