Washington (CNN) President Donald Trump is projecting optimism amid a rapidly progressing impeachment inquiry , saying Friday that the testimony released so far this week has been good for him.

"I'm not concerned about anything. The testimony has all been fine," Trump told reporters at the White House during a wide-ranging gaggle before departing for Georgia, where he is scheduled to attend a campaign fundraiser and roll out the Black Voices for Trump coalition.

Testimony from six key witnesses, including US Ambassador to the European Union Gordon Sondland , former US Ambassador to Ukraine Marie Yovanovitch and US Ambassador to Ukraine Bill Taylor, has been released in recent days. The accounts reveal remarkable consistency regarding Trump's pressure on Ukrainian President Volodymyr Zelensky to conduct an investigation into Joe and Hunter Biden and the 2016 election and the withholding of security aid contingent on Ukraine opening investigations.

Additional transcripts are expected to be released Friday.

Trump said some of those who testified were "fine" but some were "never Trumpers."

"I mean, for the most part, I never even heard of these people. I have no idea who they are. You have some very fine people, you have some never Trumpers. It seems that nobody has any firsthand knowledge ... All that matters is one thing: the transcript and the transcript is perfect," he said.

Trump said that some of the officials who have testified "really turned out to be very much honest and fair," adding that, "in no cases have I been hurt."

Sondland's revised testimony, released earlier this week, did admit a quid pro quo linking US aid to Ukraine with investigations.

The President, who previously called Sondland "a really good man and great American" and "highly respected," sought to distance himself from the onetime donor.

"Let me just tell you, I hardly know the gentleman," he said, adding, "But this is the man who said there was no quid pro quo and he still says that and he said that I said that, and he hasn't changed that testimony."

Trump's comments come in the days before the inquiry approaches a new phase, with public hearings scheduled to begin Wednesday.

The House of Representatives "shouldn't be having public hearings," Trump said, calling it a "continuation" of the "witch hunt."

House Democrats are signaling they are now on a fast-track in their impeachment proceedings, avoiding court battles that could delay their inquiry and limiting the number of witnesses at public hearings -- all signs that Trump could be impeached as soon as next month.

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He again went after the whistleblower, just one day after the whistleblower's lawyer sent a letter to the White House warning the President to "cease and desist" attacking his client.

Trump said that everything in whistleblower's report, which has been repeatedly corroborated through on-the-record testimony, "was a lie," calling for the whistleblower to "be revealed."

Trump's son has echoed that sentiment, and retweeted a tweet containing the whistleblower's name. Trump's daughter, Ivanka, however, broke with them, saying in an interview that the whistleblower's identity is "not particularly relevant."

"That is what was the catalyst for all of this discussion. But to me, it's not particularly relevant aside from what the motivation behind all of this was," she told the Associated Press during a trip to Morocco to promote her Women's Global Development and Prosperity Initiative.

On Friday, Trump's acting chief of staff Mick Mulvaney was scheduled to testify on Capitol Hill with a subpoena issued late Thursday evening. But Mulvaney did not show up. His lawyer informed investigators he would not be complying with the subpoena and asserted "absolute immunity," according to an official working on the impeachment inquiry.

Trump said he would "love to have" Mulvaney to testify, but it would have given credibility to what he has repeatedly referred to as a "hoax" and a "corrupt witch hunt."

"I like to have the people go up except it validates a corrupt investigation," he said.

He also railed against House Speaker Nancy Pelosi and House Intelligence Committee Chairman Adam Schiff, frequent targets of his ire in recent weeks as the inquiry has progressed.

Democrats, he said, are "trying to weaken me, but it's actually made me stronger," citing poll numbers and "through the roof" fundraising since the investigation began.

"Despite all that, we're kicking their ass," Trump said.