Appearing on CNN, Nadler said people shouldn't be "hung up on the semantics" since his committee is "investigating" the facts and evidence.

He said that he "wasn't waiting" for House Speaker Nancy Pelosi, D-Calif., who has been publicly reluctant to support impeachment, but added that she's been "very cooperative" with his investigation.

But after being pressed as to whether his investigation was considered "formal impeachment proceedings," Nadler insisted that's what it is.

"This is formal impeachment proceedings," Nadler said. "We are investigating all the evidence, we're gathering the evidence and we will at the conclusion of this, hopefully by the end of the year, vote to, vote articles of impeachment to the House floor or we won't. That's a decision that we'll have to make. But that -- that's exactly the process we're in right now."