President Trump confirmed to reporters on the White House South Lawn Sunday that he discussed Joe Biden and his son during a phone call with Ukrainian President Volodymyr Zelensky on July 25.

"The conversation I had was largely congratulatory, with largely corruption — all of the corruption taking place — largely the fact that we don't want our people like Vice President Biden and his son creating to the corruption already in the Ukraine and Ukraine has got a lot of problems. The new president is saying that he's going to be able to rid the country of corruption, and I said that would be a great thing, we had a great conversation."

Why it matters: Trump said on Friday that "it doesn't matter" what he discussed with Zelensky, but appeared to be more forthcoming about the call on Sunday as reports in the New York Times, Washington Post and Wall Street Journal continue to reveal new details. Some have speculated that Trump withheld military aid to Ukraine until Zelensky promised to investigate Biden and his son, but the president was adamant on Sunday that there was "no quid pro quo."

Nonetheless, Democrats have demanded that Trump release the transcript of the phone call to prove he has nothing to hide. Sen. Chris Murphy (D-Conn.) said that the "existence of an explicit quid pro quo" isn't necessary, and that if Trump "demanded a foreign government do his political bidding, that’s when he crossed the critical threshold."

that Trump release the transcript of the phone call to prove he has nothing to hide. Sen. Chris Murphy (D-Conn.) said that the "existence of an explicit quid pro quo" isn't necessary, and that if Trump "demanded a foreign government do his political bidding, that’s when he crossed the critical threshold." House Intelligence Chairman Adam Schiff (D-Calif.) , meanwhile, said that if the allegations that Trump pressured the Ukrainian government to investigate Biden are true, then Democrats may have no other choice than to impeach him.

, meanwhile, said that if the allegations that Trump pressured the Ukrainian government to investigate Biden are true, then Democrats may have no other choice than to impeach him. The backlash has done little to dissuade Trump from continuing to call for an investigation, however, as the president has spent much of the weekend tweeting about how the Democrats and "fake news media" are "protecting" Biden from the allegations. The Trump campaign on Saturday sent out an email with the subject line: "What is Joe Biden hiding?"

The big picture: It's still not known whether Trump's conversation with Zelensky is at the heart of the whistleblower complaint that has led to a standoff between House Democrats and acting Director of National Intelligence Joseph Maguire. Maguire has agreed to testify in open session next week before the House Intelligence Committee, where he is sure to face grilling over why he has refused to turn over the whistleblower complaint.

Go deeper: What you need to know about the Trump-Ukraine controversy