(CNN) 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 President Donald Trump could be impeached as soon as next month.

House Speaker Nancy Pelosi has not shared her thinking on the final timeline with her colleagues, and Democratic sources say the timing is still fluid and could continue to evolve.

But in a series of moves this week, Democrats have shown they are rapidly moving to complete the proceedings by Christmas, something that could result in Trump being just the third president to be impeached in history.

The schedule became apparent in recent days after House Intelligence Chairman Adam Schiff, a California Democrat, announced that public hearings would begin next week and also suggested Thursday there's a limit to the witnesses they would call for the public hearings.

Plus Democrats also withdrew a subpoena of a former White House official to ensure their proceedings were not delayed by a court battle. Schiff also decided Thursday not to subpoena someone who could have been a star witness -- former national security adviser John Bolton , who privately raised concerns about the Ukraine scandal at the heart of the impeachment probe. Schiff's decision came after the former Trump aide's counsel warned they would sue over any subpoena.

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