The whistleblower told Democrats that the associate had been informed by Flynn that the project was "good to go" and that the sanctions would be "ripped up".
As President Trump delivered his inaugural address, national security adviser Michael Flynn texted a former business partner that a private nuclear power project that would require lifting sanctions on Russian Federation was "good to go", a senior House Democrat said in a letter released Wednesday.
Democrats revealed the whistleblower's account in a letter sent by Rep. Elijah Cummings (D-MD) to House Oversight Chair Trey Gowdy (R-SC), which was released just as the New York Times published its own report on the claims.
The letter tells Gowdy it is hard to discern what happened because he would not subpoena Flynn, the White House, or Copson.
Flynn, who pleaded guilty last week to lying to the Federal Bureau of Investigation, was communicating with former business associates "within minutes" of Trump's inauguration, according to the letter - reassuring them Russian investments would soon be available as the Trump administration lifted sanctions.
According to a whistleblower who contacted the lawmaker, the businessman said Flynn had told him that sanctions on Russian Federation would be "ripped up" as a priority in the new Trump government to help the nuclear scheme go ahead.
The White House aide was said to have been referring to plans by a consortium of US, Russian and French companies to build and operate 45 nuclear power plants in Saudi Arabia and other Arab countries.
One of them, a proposed venture to help Middle Eastern nations build nuclear power plants with assistance from Russian Federation and the US, garnered significant press attention. According to a photo of the moment that the Democrats dug up, Flynn was standing only a few rows behind Trump and peering into his phone as the president spoke.
Cummings said the Flynn whistleblower was "extremely hesitant to come forward - and still fears retaliation" but "feels duty bound as a citizen to make this disclosure".
He called on Mr Gowdy to file legal orders to the White House, Mr Flynn and Mr Copson for documents on the nuclear power plan.
But he asked Gowdy to issue a subpoena to the White House for documents related to Flynn, saying that the committee has "credible allegations" that Flynn "sought to manipulate the course of global nuclear policy for the financial gain of his former business partners". He also lied when he said he did not recall a follow-up conversation with the ambassador, who said that "Russia had chosen to moderate its response to those sanctions as a result of Flynn's request". The whistleblower isn't named, but Cummings promised in the letter to share the person's identity with Gowdy if it remains confidential and Gowdy agrees to speak with the whistleblower.
Copson allegedly told those around him that "Mike [Flynn] has been putting everything in place for us". White House lawyer Ty Cobb said, "I respectfully decline to comment on anonymous information which impacts the Special Counsel investigation".
"I believe the American people want Congress to hold President Trump and his administration accountable", Cummings wrote, "and they are exhausted of Republicans in Congress putting their heads in the sand when faced with credible allegations of grave abuses".