The White House is tense — and some aides are frantic — as Democrats on Capitol Hill tap a gusher of revelations that paint an increasingly vivid portrait of President Trump's unrestrained conduct of foreign policy.

Why it matters: Democrats are moving fast. Letters to potential witnesses reveal the breadth and speed at which the inquiry is unfolding, a stark contrast to the Mueller report which stretched over nearly two years.

The probe now reaches into the Pentagon, with Democrats sending a letter demanding the appearance of Acting Assistant Defense Secretary for International Security Affairs Kathryn Wheelbarger.

Fiona Hill, Trump's former National Security Council senior director for Europe and Russia, testified yesterday that then-national security adviser John Bolton told her to notify the NSC's chief lawyer about a rogue effort by EU ambassador Gordon Sondland, Rudy Giuliani and acting White House chief of staff Mick Mulvaney, the N.Y. Times reports.

"I am not part of whatever drug deal Sondland and Mulvaney are cooking up," Bolton instructed Hill to tell White House lawyers, according to the Times.

"Giuliani’s a hand grenade who’s going to blow everybody up," Hill, during 9+ hours behind closed doors at the House Intelligence Committee, quoted Bolton as saying.

Some White House officials are demoralized, amid unusual chaos and uncertainty, even for this West Wing, according to a former top Trump official.

"Others ... are girding for a fight and confident in their boss and the likely political outcome," the official said.

Mulvaney has complained to people that White House counsel Pat Cipollone is developing the impeachment legal strategy with Trump and not sharing information with key staff.

Mulvaney and Cipollone, Trump's two most vital strategists for impeachment, aren't getting on, as documented by the Times and others.

And tensions are rising between Cipollone and those who think he has been playing this wrong.

At the other end of Pennsylvania Avenue, House Democrats tell Axios that every witness has bolstered the case against Trump, with what Democrats contend is little contradictory evidence. Our takeaways:

If everyone agrees to appear, Democrats will have interviewed 11 Trump administration officials by the end of next week.

The people and agencies being called to Capitol Hill have now expanded to the White House Office of Management and Budget acting director Russ Vought, the Defense Department and Giuliani associates.

And the daylong appearances by Hill — as well as former Ukraine envoy Kurt Volker, and former ambassador to Ukraine Marie Yovanovitch — show House investigators are being incredibly thorough in their questioning.

Democratic committee sources say Pelosi still maintains that their investigation needs to wrap by the end of the year.

Final bit of intrigue: Dems tell Axios that this week's depositions are private partly to prevent other witnesses from coordinating or aligning their testimony with what others say.

But they plan to release many transcripts to the public in the future.

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This piece includes additional reporting by Zachary Basu.