In 2013, I filibustered the nomination of CIA Director John Brennan. I did so to defend a core constitutional principle that has made America a leader among nations for as long as we have been a nation–the right to due process.

I wanted to know if President Obama believed he had the power to kill an American citizen without due process. It took me almost 13 hours to get my answer, but the Obama Administration finally relented.

They seemed annoyed I had even asked the question. I was flabbergasted that it took them so long to answer it.

I’m still not sure they completely get the message.

President Obama’s nomination of Judge David Barron to the U.S. 1st Circuit Court of Appeals is troubling because it relates directly, again, to the issue of whether this Administration believes we have a Fifth Amendment.

In 2010, Barron was the head of the Office of Legal Counsel, a group that dispenses legal advice to executive branch agencies. That year, Barron circulated a memo that authorized the extra-judicial killing of two American citizens, radical Yemeni cleric Anwar al-Awlaki and Islamic extremist Samir Khan. Both would be assassinated by a CIA drone the following year.

I have no sympathy for al-Awlaki, Kahn, or others like them. But that does not mean the president or anyone else in government has the authority to kill an American citizen without due process where there isn’t an imminent threat.

Awlaki had been on a presidential “kill list” before his death, something Senator Ron Wyden had been trying to determine the legal rationale for. Sen. Wyden waited for over a year to see the Barron memo, and it was never fully disclosed.

To date, over 30 members of Congress have made multiple attempts to see this memo, and most have never seen it.

What is this Administration trying to hide?

On April 21, 2014, the U.S. Court of Appeals for the 2nd Circuit ordered that the Department of Justice disclose a redacted version of the Office of Legal Counsel memorandum that authorized the targeted killing of Anwar al-Awlaki. David Barron was one of the principal writers of this memorandum. He has spoken openly about his role in crafting the Administration’s legal position that it can kill Americans abroad without due process.

It would be irresponsible for the Senate to move forward on this nomination until the Department of Justice has complied with the court order to disclose this document, which will highlight Barron’s views on international law, the Fifth Amendment and its guarantee of due process, and the civil liberties of our nation’s citizens.

The right to due process is not some negotiable aspect of our Constitution, subject to the whim of whoever happens to be sitting in the Oval Office.

The Bill of Rights existed long before President Obama was elected, and as long as I’m a U.S. Senator, I will fight to protect the basic rights and liberties that belong to all of us as American citizens.

When I talk with our brave young men and women who have sacrificed so much for their country, many of whom have lost limbs, they understand that they were fighting to defend the Constitution and the Bill of Rights.

It dishonors their service and sacrifice to find that upon their return home, we are not honoring due process and the right to trial by jury.

Such legal protections are quintessential to our most basic freedoms, dating all the way back to the Magna Carta. Our constitutional rights are not negotiable.

America has always been a nation of laws, not of men, and any man who thinks himself above the law–including the president–must be reminded of this in no uncertain terms.

Until that memo is made public, I will do everything in my power to stop David Barron’s nomination to the 1st Circuit Court of Appeals.