House Democrats are looking into a second phone call made between President Donald Trump and Ukraine President Volodymyr Zelensky as part of an impeachment investigation that has upended the administration.

The call in question took place on April 21 of this year, shortly after Zelensky won election. There is no apparent White House read out of what was discussed between the two world leaders, but foreign press reports said it was congratulatory.

The call has been the subject of intense rumors and fascination for days, as more information has been made public about the pressure that Trump exerted on Zelensky to look into largely discredited allegations of corruption involving former Vice President Joe Biden and his son, Hunter. Now the call is of keen interest to Democrats on Capitol Hill who last month launched an investigation into President Trump and Giuliani and their overtures to Ukraine about Biden, a congressional aide told The Daily Beast. A source on the House Intelligence Committee, which is involved in the investigation, told The Daily Beast on Wednesday that officials were “aware of this call” and “obviously following up on it.”

Congressional Democrats may not encounter much resistance as they look into the April 21 call. In a press conference Wednesday at the Intercontinental Hotel in New York, Trump said he would release the transcript of his first discussion with the Ukrainian president.

“I can save you a lot of time, they were all perfect,” Trump said, referring to his calls with Zelensky.

Should Trump follow through on that promise, it would mark the second case of him revealing details of his previously private discussions with Zelensky. Earlier on Wednesday, the White House released a detailed memorandum of a July 25 call between the two leaders, in which it was revealed that Trump asked Zelensky to look into the Biden allegations and to touch base with his personal attorney, Rudy Giuliani, and the attorney general, Bill Barr, on the matter.

Giuliani’s role has been of particular interest to House Democrats. The Daily Beast first reported that lawmakers were preparing an investigation into Giuliani’s activities in Ukraine, among which involved efforts to dig up dirt on Biden. Then, last month, the House Foreign Affairs, Intelligence, and Oversight committees launched an official investigation into President Trump and Giuliani, saying they would look into whether Giuliani’s communications with Ukraine threatened U.S. foreign policy interests. The committees also said they would probe Trump’s temporary decision to withhold aid from Ukraine.

Those investigations have now been accelerated with the announcement of House Speaker Nancy Pelosi on Tuesday that the party would begin formal impeachment proceedings.