This is a lower-court ruling, with appeals doubtless to follow at the circuit level and maybe before the Supremes, so there’s still a lot of legal ball here left to be played.
But House Democrats wanted to win this one, hoping that a ruling against Trump on executive privilege might jar loose some of the key Ukraine witnesses who had been ignoring subpoena until now. Don McGahn’s subpoena was issued during the Russiagate probe, not the Ukraine matter, but obviously any new rule involving testimony for the former will apply to the latter, probably more forcefully given that the House has invoked its impeachment power in investigating Ukraine.
The judge, Ketanji Brown Jackson, is an Obama appointee, a fact Trump will doubtless note once he tweets about this. But in the meantime, the White House’s “absolute immunity” defense to House subpoenas is shattered. The key section addressing presidential power to defy Congress on grounds of executive privilege begins on page 102 of the decision. Certainly, says Jackson, McGahn may have valid grounds to hold back certain information as privileged while testifying. But to refuse to appear altogether on the theory that Congress can’t compel an executive-branch employee to speak if the president doesn’t approve? Nope: