WASHINGTON – The whistleblower who filed an anonymous complaint about President Donald Trump asking Ukraine to investigate a political rival has reached an agreement to testify before Congress, Rep. Adam Schiff announced Sunday.

Talking with ABC News' "This Week," Schiff, the Democrat who chairs the House Intelligence Committee, said the whistleblower would testify "very soon" and the only thing standing in the way was getting security clearances for the attorneys representing the whistleblower so they could attend the testimony.

The whistleblower, whose identity has not been made public, revealed deep concern that Trump “used the power of his office” to solicit Ukraine’s help to discredit one of his main political rivals, former Vice President Joe Biden.

The complaint went on to detail efforts by senior White House officials to later "lock down" access to all records of the July 25 call with Ukrainian President Volodymyr Zelensky in which Trump urged his counterpart to investigate Democratic presidential candidate Biden and his son Hunter Biden.

The whistleblower's concerns were the tipping point for House Democrats, who formally launched an impeachment inquiry into Trump this week after months of investigating the administration and conduct of the president.

Schiff did not outline a date for testimony and the whistleblower's attorneys said in a statement that they continue to work with the House and Senate about finalizing logistics, adding no date has been set.

Congress is on a two-week recess, but the impeachment inquiry doesn't appear to be slowing down. On Friday, Schiff announced a number of depositions scheduled with State Department officials and a private hearing with the intelligence community's inspector general, the official who received the whistleblower complaint and found it credible and urgent. Schiff also announced Secretary of State Mike Pompeo was being subpoenaed for documents related to the Trump-Ukraine episode.

Schiff said Sunday that the biggest concern with having the whistleblower appear before Congress was protecting the person's identity, noting comments made by Trump at a private event where he suggested the whistleblower had committed treason and should be punished.

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"You know what we used to do in the old days when we were smart with spies and treason, right?" Trump said, according to published reports. "We used to handle it a little differently than we do now."

Schiff said there were a number of "security concerns" that were being worked out to protect the person.

"We are taking all the precautions we can," he said, so that the congressional panel allows the "testimony to go forward in a way that protects the whistleblower's identity."

Throughout the week, a series of developments have deepened this controversy, including the public release of the complaint and a summary of the call Trump had with Ukraine's president.

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Some Republicans have signaled concern as the details have continued to mount, though no congressional Republicans have come out in support of ousting Trump from office.

Trump's former homeland security adviser Tom Bossert on Sunday acknowledged the reports were not good news for the president.

"It is a bad day and a bad week for the president and for this country if he is asking for political dirt on an opponent," he told "This Week" anchor George Stephanopoulos.

But, Bossert, who left the administration in April, noted that the allegations lodged against Trump were "far from proven," especially when it comes to whether military aid was being kept from Ukraine in exchange for an investigation into Biden. He urged caution and a refrain from rushing to judgment.

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Bossert voiced frustration, specifically, for Trump's personal attorney Rudy Giuliani, who went to Ukraine multiple times to investigate Biden and a theory that Ukraine meddled in the 2016 elections. Bossert said he explained to Trump multiple times that this theory was "not only a conspiracy theory, it is completely debunked."

"I am deeply frustrated with what (Giuliani) and the legal team is doing and repeating that debunked theory to the president," Bossert said. "It sticks in his mind when he hears it over and over again."

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