The White House tried to use a fake thing called "absolute immunity" to prevent Don McGahn from testifying in front of the House of Representatives. Well, a judge formally ruled that this immunity isn't a thing and McGahn must comply with the subpoena...except he can invoke executive privilege, if needed.
Trump's lawyers initially claimed that all former White House staff and presidential advisers are “absolutely immune” from congressional subpoena. Judge Jackson was clearly not swayed. McGahn is a potential witness to Donald Trump's efforts to obstruct justice in the Mueller investigation, as well as potential other crimes.
We will update this post as more details come out.