In a rare moment of bipartisanship, the Senate voted unanimously for a whistleblower complaint involving President Donald Trump to be turned over to congressional intelligence committees.

The move is monumental, and it came as House Speaker Nancy Pelosi announced her support of a formal impeachment inquiry into Trump stemming from the complaint.

The complaint centers around a July 25 phone call Trump had with Ukrainian President Volodymyr Zelensky in which Trump reportedly pressured Zelensky to work with his personal lawyer Rudy Giuliani to investigate former Vice President Joe Biden ahead of the 2020 election.

The whistleblower also alleges that Trump made a "promise" to Zelensky during the call, but it's unclear what the promise was.

The whistleblower is in talks with both congressional intelligence committees about testifying in regard to their complaint against Trump.

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The Senate voted unanimously in favor of a resolution on Tuesday calling for a whistleblower complaint involving President Donald Trump to be turned over to congressional intelligence committees.

The move is monumental and a rare moment of bipartisanship between Democrats and Republicans in the upper chamber. It also came as House Speaker Nancy Pelosi was expected to announce her support of a formal impeachment inquiry into Trump stemming from the whistleblower's complaint.

According to recent reports, the complaint centers around a phone call Trump had with Ukrainian President Volodymyr Zelensky, during which Trump pressed Zelensky to investigate former Vice President Joe Biden's dealings in Ukraine ahead of the 2020 election, according to The Wall Street Journal.

The Wall Street Journal reported that Trump pressured Zelensky to work with his personal lawyer Rudy Giuliani on the matter at least eight times during their July 25 phone call. The whistleblower's complaint also references a "promise" that Trump made to Zelensky, but it's unclear what it was, The Washington Post reported last week.

Media reports have said it could relate to a nearly $400 million military-aid package that the Trump administration slow-walked until a few days after the complaint was filed.

The Washington Post reported on Monday that Trump decided to slam the brakes on sending the aid roughly a week before his call with Zelensky and released it on September 12 after Schiff requested a full, unredacted copy of the whistleblower's complaint.

The president confirmed The Post's reporting on Tuesday and said he decided to withhold the aid days before the call with Zelensky, but he denied that it was part of any quid pro quo effort. Instead, he said his main concern with sending military assistance to Ukraine was that other countries haven't been paying their fair share as well.

But he appeared to acknowledge on Monday that the aid package was at least somewhat on his mind during the call with Zelensky.

"It's very important to talk about corruption," Trump said. "If you don't talk about corruption, why would you give money to a country that you think is corrupt? It's very important that on occasion, you speak to somebody about corruption."

Read more: A mysterious exchange between Trump and a foreign leader is Washington's latest obsession. Here's what's actually going on.

Democratic Rep. Adam Schiff, the chairman of the House Intelligence Committee, first revealed the existence of the complaint on September 13, when he subpoenaed acting Director of National Intelligence Joseph Maguire to turn over the full complaint to the committee in accordance with federal law.

The intelligence community inspector general determined that the complaint was credible and a matter of "urgent concern." But the Office of the Director of National Intelligence overruled the inspector general after consulting with the Justice Department and concluded that the complaint did not fit the definition of "urgent concern" under federal law.

The definition concerns serious allegations related to "the funding, administration or operation of an intelligence activity within the responsibility and authority" of the director of national intelligence, Jason Klitenic, the Office of the Director of National Intelligence's general counsel, wrote in a letter to Schiff.

"This complaint, however, concerned conduct by someone outside the Intelligence Community and did not relate to any 'intelligence activity' under the DNI's supervision," Klitenic added. For that reason, after consulting with the Justice Department, the agency concluded it was not required to forward the complaint to the intelligence committees.

On Tuesday, Politico reported that the whistleblower and their attorney were in talks with the House and Senate intelligence committees to testify about the complaint.

The House panel has "been informed by the whistleblower's counsel that their client would like to speak to our committee and has requested guidance from the Acting DNI as to how to do so," Schiff tweeted.

He added: "We're in touch with counsel and look forward to the whistleblower's testimony as soon as this week."

Democratic Sen. Mark Warner, the vice chairman of the Senate Intelligence Committee, also confirmed to Politico that the whistleblower's lawyer had reached out but added, "We're going to have to take this one step a time. And I think it's terribly important to get the facts."