A D.C. appeals court on Friday allowed House Democrats to continue their case for testimony from former White House counsel Don McGahn before the House Judiciary Committee.

Why it matters, via the AP:McGahn was one of the most important witnesses in Robert Mueller's investigation. He appears on 66 pages of the Mueller report and played a central role in some of its juiciest revelations, including the fact that President Trump once asked him to fire Mueller.

Catch up quick: Democrats on the House Judiciary Committee have fought a lengthy legal battle to question McGahn regarding Trump's alleged attempts to obstruct justice.

What's next: The matter now returns to a three-judge panel for consideration on other legal issues.

• Worth noting: Judge Thomas Griffith noted in his dissent that "the chances that the committee hears McGahn’s testimony anytime soon are vanishingly slim," since the current House session ends at the start of January.

Read the ruling.

Go deeper: Former White House counsel Don McGahn off the record