U.S. President Donald Trump appears to have admitted Sunday that he did talk to Ukrainian President Volodymyr Zelensky about unsubstantiated corruption allegations against former Vice President Joe Biden and his son.

The admission came after days of news reports, allegations, stonewalling, and denials about claims that the president threatened to withhold military aid to Ukraine as leverage to force Zelensky to launch a probe that could damage one of his main rivals in next year’s election.

“The conversation I had was largely congratulatory, was largely corruption, all of the corruption taking place, was largely the fact that we don’t want our people like Vice President Biden and his son [contributing] to the corruption already in Ukraine,” Trump told reporters Sunday.

But the president insisted that he did “absolutely nothing wrong” in the call, adding that the conversation was "perfect.”

The president once again leveled the same unsubstantiated allegations against Biden on Twitter on Sunday night:

Trump’s concession came only after the Wall Street Journal reported that the president had pressed Zelensky up to eight times to work with his lawyer Rudy Giuliani to investigate allegations against Biden and his son.

Trump and his allies have claimed, without providing any evidence, that Biden used his position as vice president to pressure Ukraine into firing a prosecutor who was investigating possible criminal charges against Biden’s son Hunter, who was on the board of Burisma Holdings, a major Ukrainian energy company.

There is no evidence of wrongdoing by Biden or his son, and a Ukrainian prosecutor general said in May that the company did not violate Ukrainian law by having Hunter Biden in a paid position on its board.

The phone call with Zelensky, which formed part of a complaint by an intelligence community whistleblower, took place on July 25. That was prior to the U.S. approving $250 million in military aid to Ukraine, though CNN reports that this was not explicitly mentioned during the call and Trump said Sunday there was “no quid pro quo” in his calls for an investigation.

The White House and the Department of Justice have so far refused to release the transcripts of the call despite demands to do so from Congress.

Biden, speaking on the campaign trail at the Iowa Steak Fry, said he never discussed any overseas business dealings with his son, and called for Trump to be investigated. “He’s using the abuse of power and every element of the presidency to try to do something to smear me,” Biden told reporters Saturday.

Democratic House Speaker Nancy Pelosi called the scandal “a new level of lawlessness” on Sunday night, as calls for impeachment among Democrats grew.

Adam Schiff (D-CA), an influential Democrat who heads the House Intelligence Committee and has so far resisted calls for impeachment, said Sunday on CNN that the House may have “crossed the Rubicon” with Trump’s admission and his continuing refusal to release the transcripts.

Pelosi has been highly reticent to even mention the word “impeachment” in recent months, but in a letter to fellow House Democrats Sunday she hinted that the latest scandal could be the final straw.

“If the administration persists in blocking this whistleblower from disclosing to Congress a serious possible breach of constitutional duties by the president, they will be entering a grave new chapter of lawlessness which will take us into a whole new stage of investigation,” Pelosi wrote.