WASHINGTON — President Donald Trump’s first national security adviser, Michael Flynn, texted a former business associate on Inauguration Day that Obama-era sanctions against Russia would be “ripped up” and that a lucrative proposal to build nuclear reactors with Russian partners in the Middle East was “good to go,” a witness has told Congress.

Rep. Elijah Cummings of Maryland, the top Democrat on the House Oversight and Government Reform Committee, made a letter public Wednesday that described the unidentified person’s account.

Cummings said he had spoken to the witness and called the account a “credible” allegation that Flynn “sought to manipulate the course of international nuclear policy for the financial gain of his former business partners.”

Flynn pleaded guilty Friday to lying to the FBI about his discussions with the Russian ambassador about sanctions during the transition. It’s unclear if the new claim puts him in additional legal jeopardy.

Flynn is cooperating with prosecutors as part of his plea agreement with Robert Mueller, who is heading the probe into possible collusion between the Trump campaign and Russian meddling in the election.

Cummings detailed the witness’ allegations in a letter to House Oversight Chairman Trey Gowdy, R-S.C., and urged Gowdy to authorize subpoenas to Flynn and his associates to learn more about his efforts to aid the proposal.

Flynn was ousted as national security adviser after only 24 days on the job. The administration has not lifted sanctions on Russia.

The news about Flynn came as the president’s oldest son, Donald Trump Jr., refused to tell lawmakers about conversations he had with his father regarding a 2016 meeting with a Russian lawyer after emails detailing the meeting had become public, according to the top Democrat on the House intelligence committee.

Speaking to the committee behind closed doors on Wednesday, Trump Jr. said he didn’t tell the president about the meeting when it happened and he declined to elaborate on what he ultimately told him after the meeting became public.

California Rep. Adam Schiff said that Trump Jr. said he couldn’t speak about the conversations with his father because of attorney-client privilege, telling the committee a lawyer was present when he spoke to his father.

Associated Press contributed.

david.cloud@latimes.com