Washington: Days after a decorated Army lieutenant colonel offered damaging testimony about President Donald Trump’s conduct on a July phone call with Ukraine’s leader, Trump stood on the South Lawn and issued a vague but ominous warning.

“You’ll be seeing very soon what comes out,” Trump said Saturday, referring to the officer, Lt. Col. Alexander Vindman.

Trump was not more specific. But an attack on Vindman’s character and motives was already making its way from the dark corners of Trump’s social media following to the front lines of the impeachment battle.

One day earlier, right-wing commentator Jack Posobiec had retweeted a lengthy thread by a Florida man - a fan of QAnon, a fringe conspiracy about the “deep state” - claiming to have witnessed Vindman “bash America” in a conversation with Russian officers during a joint military exercise in Germany in 2013.

That accusation was unsubstantiated and has been rejected by some of the colonel’s colleagues. Even so, Posobiec’s post was retweeted by Trump’s son and chief defender, Donald Trump Jr., driving it through conservative social media circles and onto pro-Trump websites, whose stories the younger Trump promoted to his 4 million followers.

“Anyone who’s been watching for the past three years is not at all surprised that this would be their ‘star witness,’” Donald Trump Jr. posted about Vindman, who had testified that he was concerned about the United States’ linking of military aid to Ukraine with an investigation of Trump’s political rival.

While the White House has scrambled to mount an organised response to the House impeachment inquiry - there is no consistent message from Trump’s team and little formal guidance to surrogates - Twitter has become the president’s war room. The president and his supporters, including his family, have used Twitter to frame his defence, torch his Democratic inquisitors and try to undermine public officials, like Vindman, who have testified against him.

It is hard to discern how the 6-year-old comments attributed to the officer affect the veracity of his testimony on Capitol Hill, which aligns with that of numerous other witnesses. But by questioning the colonel’s loyalties, partisans who are spreading the story uncritically to millions of Americans leave the impression he is somehow not to be believed.

The attack emerged late on Halloween night, when a retired Army officer, Jim Hickman, claimed he had overheard Vindman - a major at the time who was chatting with Russian soldiers during a military exercise - laugh “about Americans not being educated or worldly” and talking up “Obama & globalism to the point of uncomfortable.” Hickman said he took the major aside and reprimanded him.

Through his lawyer, Michael Volkov, Vindman declined to comment.

Hickman, a former lieutenant colonel whose service record indicates he served in Afghanistan and earned a Purple Heart, at some point took an interest in QAnon. A review of his past tweets found more than 100 in which he recirculated or commented on QAnon-related theories, including hoaxes about Satanism and pedophilia, and until recently he had the hashtag #Q in his profile. Reached for comment, Hickman said he did not believe in QAnon but found it “interesting.”

“I do think it’s actually been pretty accurate on predicting a lot of things,” he said.

He has also tweeted strident pro-Trump, anti-Democratic themes, writing, “It’s incredible how evil the Democrat party is.” A week before going public with his story about Vindman, he retweeted a Trump supporter urging “STOP IMPEACHMENT! STOP THIS COUP!”

In a Twitter thread, Hickman, who said he was disabled from combat injuries and living in Florida, said he had helped manage joint exercises in Germany involving U.S. and Russian soldiers. He met Vindman there in 2013, he said.

Vindman referred to himself as a patriot during closed-door testimony in the House last month and said he had reported concerns about the president and his inner circle’s conduct out of a “sense of duty.” The colonel received a Purple Heart after being injured by an improvised explosive device in Iraq.

Several officials have publicly defended Vindman since his testimony emerged. Gen. Joseph Dunford, the former chairman of the Joint Chiefs of Staff, has called the colonel “a professional, competent, patriotic and loyal officer.” Michael McFaul, the former ambassador to Russia, has said he had worked with the colonel “and interacted with him in front of Russian officers. He never once said anything near what this ‘retired Army officer’ claims.”