"Conducting investigations is the means that Congress uses to carry out that constitutional obligation. Thus, blatant defiance of Congress’ centuries-old power to compel the performance of witnesses is not an abstract injury, nor is it a mere banal insult to our democracy. It is an affront to the mechanism for curbing abuses of power that the Framers carefully crafted for our protection, and, thereby, recalcitrant witnesses actually undermine the broader interests of the People of the United States."

“Unfortunately for DOJ... these contentions about the relative power of the federal courts, congressional committees, and the President distort established separation-of-powers principles beyond all recognition. Thus, ultimately, the arguments that DOJ advances to support its claim of absolute testimonial immunity for senior-level presidential aides transgress core constitutional truths...”

“Stated simply, the primary takeaway from the past 250 years of recorded American history is that Presidents are not kings. ...This means that they do not have subjects, bound by loyalty or blood, whose destiny they are entitled to control. Rather, in this land of liberty, it is indisputable that current and former employees of the White House work for the People of the United States, and that they take an oath to protect and defend the Constitution of the United States. Moreover, as citizens of the United States, current and former senior-level presidential aides have constitutional rights, including the right to free speech, and they retain these rights even after they have transitioned back into private life.”

“ith respect to senior-level presidential aides, absolute immunity from compelled congressional process simply does not exist. Indeed, absolute testimonial immunity for senior-level White House aides appears to be a fiction that has been fastidiously maintained over time through the force of sheer repetition in OLC opinions, and through accommodations that have permitted its proponents to avoid having the proposition tested in the crucible of litigation. And because the contention that a President’s top advisors cannot be subjected to compulsory congressional process simply has no basis in the law, it does not matter whether such immunity would theoretically be available to only a handful of presidential aides due to the sensitivity of their positions, or to the entire Executive branch. Nor does it make any difference whether the aides in question are privy to national security matters, or work solely on domestic issues.”

“Thus, DOJ’s hand-waving over the Judiciary Committee’s purported failure to establish a “cognizable” injury for standing purposes... masks the substantial harm that results from an Executive branch official’s defiance of a congressional subpoena. But it is hard to imagine a more significant wound than such alleged interference with Congress’ ability to detect and deter abuses of power within the Executive branch for the protection of the People of the United States.”

“owever busy or essential a presidential aide might be, and whatever their proximity to sensitive domestic and national-security projects, the President does not have the power to excuse him or her from taking an action that the law requires. Fifty years of say so within the Executive branch does not change that fundamental truth. Nor is the power of the Executive unfairly or improperly diminished when the Judiciary mandates adherence to the law and thus refuses to recognize a veto-like discretionary power of the President to cancel his subordinates’ legal obligations.”

“This Court holds that Executive branch officials are not absolutely immune from compulsory congressional process—no matter how many times the Executive branch has asserted as much over the years—even if the President expressly directs such officials’ non-compliance.”