The latest damning revelation in the Trump-Russia saga is that Trump Jr failed to disclose that he met Rinat Akhmetshin, a former Soviet counter-intelligence officer, during his father’s election campaign.

Numerous sources, including Mr Akhmetshin himself and a spokesman for Trump Jr, confirmed to US media at the weekend that the former Russian officer was in the room.

A steady drip of leaks and admissions over the past week have uncovered increasingly suspicious information about the June 2016 meeting at Trump Tower in Manhattan.

The meeting appears to be the most tangible evidence of a connection between Mr Trump’s election campaign and Russia.

The scandal is taking its toll. The latest ABC News/Washington Post poll gave Donald Trump an approval rating of only 36 per cent, down from 42 per cent in April. That’s the lowest six-month rating of any US president since the poll began 70 years ago.

President Trump hit back on Sunday night with his usual retort of “Fake News”.

Mr Trump Jr’s account of the meeting has changed almost daily.

At first, the meeting was said to be about a Russian adoption program. Then, it was to hear information about campaign rival Hillary Clinton.

Finally, Mr Trump Jr was forced to release emails – mere moments before The New York Times planned to do so – that revealed he had told an associate that he would “love” Russia’s help in obtaining negative details about the Democratic presidential candidate.

In the room were the President’s son, Trump Jr; his son-in-law, Jared Kushner; and his former campaign adviser, Paul Manafort.

Initial reports suggested the trio had solely met with a Russian lawyer, Natalia Veselnitskaya.

Then, Russian-born translator Anatoli Samochornov and publicist Rob Goldstone got added to the list. Finally, we learned former Soviet officer Rinat Akhmetshin was also there, bringing the current tally to seven.

Incredibly, CNN has reported there were “at least eight” in the room. The name of the eighth person is yet to be confirmed.

Mr Akhmetshin’s alleged criminal history makes his presence the most explosive revelation yet.

The Daily Beast reported that court papers filed with the New York Supreme Court in 2015 by Russian mining company International Mineral Sources allege that Mr Akhmetshin orchestrated the hacking theft of confidential information from the company’s computers. The allegations were later withdrawn.

Mr Akhmetshin – who now works as a pro-Moscow lobbyist in Washington DC – denied to NBC News he still had ties to Russian intelligence. He told the Associated Press he served in a Soviet military counter-intelligence unit but was never formally trained as a spy.

A 2016 Radio Free Europe report alleged that Mr Akhmetshin’s lobbying efforts included a smear campaign against Russian MP Ashot Egiazaryan when he sought political asylum in the US.

Earlier this year, Republican Senator Charles Grassley wrote to Homeland Security secretary John Kelly describing Mr Akhmetshin as “a Russian immigrant to the United States who has been accused of acting as an unregistered agent for Russian interests and apparently has ties to Russian intelligence”.

The Russian lawyer, Ms Veselnitskaya, has denied having any ties to the Kremlin and is insisting the purpose of the meeting was to discuss US sanctions against Russia, not the presidential campaign.

After the latest revelation, Mr Trump Jr, through his lawyer Alan Futerfas, said he knew nothing of Mr Akhmetshin’s background at the time of the meeting.

On Saturday it was revealed that President Trump’s political campaign – rather than his family – has paid $US50,000 ($A63,735) to Mr Futerfas’ law firm for “legal consulting” fees. This effectively means Trump supporters are funding his son’s defence.

Mr Trump Jr did not mention Mr Akhmetshin’s presence when he released the emails earlier this week, despite telling Fox News on July 11: “This is everything. This is everything.” He has not explained this discrepancy.

Accusations by US intelligence agencies that Moscow meddled in the election and colluded with the Trump campaign have dominated the Republican President’s first months in office.

US intelligence agencies said earlier this year that Russia sought to help President Trump by hacking private emails from Democratic Party officials and disseminating false information online.

– with AAP