“A longtime career employee at the White House Office of Management and Budget is expected to break ranks and testify Saturday in the House Democrats’ impeachment inquiry, potentially filling in important details on the holdup of military aid to Ukraine.

“Mark Sandy would be the first OMB employee to testify in the inquiry, after OMB acting director Russell T. Vought and two other political appointees at the agency defied congressional subpoenas to appear. The White House has called the impeachment inquiry unconstitutional and ordered administration officials not to participate.”

Keep in mind that the head of the Office of Management and Budget is none other than Mick Mulvaney, who is also currently serving as acting White House chief of staff. And it turns out that Mulvaney has played a critical role in the Ukraine scandal, as we first learned earlier this month when The Daily Beast reported that OMB placed a “pause” on the sale of Javelin anti-tank missiles to Ukraine:

“The unusual move didn’t just foreshadow the huge fight that has President Donald Trump now facing impeachment. It also caught the eye of congressional investigators in the impeachment inquiry.”

Since Mulvaney has steadfastly refused to appear before the impeachment committee — (he’s asking a federal judge to rule that he has “absolute immunity) — Sandy will likely be able to explain why OMB placed a hold on the weapons Ukraine desperately needed to defend itself from Russian aggression. And that explanation will probably implicate Mulvaney and even the president himself.

Saturday will be a closed-door deposition with Sandy, but as we’ve seen with others who have fist given depositions, Sandy will eventually testify in public. And that could wind up being devastating for Mulvaney, Trump, and the entire Trump administration.

Things are getting more interesting by the day.