Hope Hicks, Trump’s then-communications director, appeared before the House Intelligence Committee for a voluntary nine-hour interview this week.

The headline was that she admitted having told white lies on behalf of Trump, but never lied about matters material to the Russia investigation. That leaves us with the head-scratching conundrum of what to believe when a liar admits to lying on behalf of a liar, but insists the lies were not material to the investigation. The questions abound. What is the difference between a material lie and a white lie? If an admitted liar insists her lies were not material, is she lying? Is that a white lie or a material lie? How does she know whether or not her lies were material unless she knows the full scope of the investigation? And, of course, why is a 29-year old public relations flack with a background in fashion the White House communications director?

Well, she no longer is. Her surprise resignation the day after her congressional interview raises another host of questions. She was one of Trump’s closest advisors and has stories to tell. She was also interviewed by Mueller in recent weeks. The combination of Mueller and congressional questioning may have brought home to her how precarious her situation is. Her admission that she lied on Trump’s behalf would have been disqualifying in most administrations, but seems normal for the Trump administration. Maybe she simply realized it was time to get out.

Regardless, her appearance in the House Intelligence Committee highlighted the success of the Republican majority in colluding with the White House to thwart the committee’s ability to conduct a credible investigation. Even putting aside the clownish, inept, and bad-faith conduct of the supposedly recused committee chair, Devin Nunes, the committee has repeatedly embarrassed itself. Nunes’s stunts of running to brief the president about information the president’s people had given him and then issuing a thoroughly discredited memo criticizing the FISA warrant process are a distraction to the true scandal in the committee. By coddling witnesses and refusing to invoke the committee’s full powers, the Republican majority has failed in its constitutional obligation to check the executive branch and its institutional obligation to expose the Russian assault on our democracy. Instead, it has chosen to circle the wagons around a lying and corrupt president.

The Constitution contemplates a robust role for Congress in investigating the executive branch. The Constitution gives Congress power to remove the president and other executive officers through impeachment and to investigate any matter that is relevant to its legislative duties. In aid of these functions, Congress has the power to hold hearings, summon witnesses, and hold in contempt witnesses who don’t comply. Sadly, the Republican Congress has refused to use these tools, instead relying on watered-down procedures that favor witnesses and protect the president. This criticism applies most harshly to the House Intelligence Committee, but others are not exempt.

The House Intelligence Committee has fallen back on closed-door, voluntary witness interviews as its principal investigatory tool. Without more, they are virtually worthless. The public never sees the witness, and learns of the testimony through the occasional leak or in rare instances when the committee releases a transcript. Because witnesses appear voluntarily, they are free to answer only questions they like and terminate the interview at any time. While it is a crime to lie to congressional investigators, it is not a crime to refuse to answer. In other contexts, these interviews are used productively as discovery for public hearings at which the witness must face the bright lights and will be embarrassed by repeated refusals to answer questions and suspicious lapses of memory. Republicans, however, have refused to hold follow-up public hearings.

Hope Hicks, we are told, refused to answer any questions regarding the period after Trump’s inauguration and answered only selectively questions about the campaign and transition.

Traditionally, reluctant witnesses are compelled to appear before a committee by subpoena. Failure to appear can result in contempt of Congress. Witnesses appearing pursuant to subpoena must answer questions unless they assert a valid privilege. There are only two that a committee must recognize by law: the privilege against self-incrimination and executive privilege.

Any witness appearing under compulsion may assert a Fifth Amendment privilege against self-incrimination. For prominent witnesses, however, taking the Fifth in a public hearing comes with a substantial cost. It appears cowardly and is inevitably, though improperly, interpreted as an admission of guilt. A witness appearing voluntarily, such as Hicks, can simply refuse to answer and need not assert the Fifth Amendment.

Consider the difference between Donald Trump Jr. being asked 1) in a voluntary closed session and 2) under subpoena in a public hearing about the substance of the June 9, 2016 Trump Tower meeting with Russians. In the voluntary closed session he could simply refuse to answer, angering a few Democratic members who couldn’t do anything about it. Under subpoena in a public hearing, he would most likely have to take the Fifth for the entire country to hear.

Executive privilege was first recognized by the Supreme Court in Nixon’s losing attempt to conceal the Watergate tapes. The privilege, which has special force regarding national security and law enforcement, shields communications between the president and his advisors regarding the president’s performance of his non-delegable functions. It can also apply to conversations between his advisors and people they consult to assist in advising the president.

The privilege is not absolute. The needs of a grand jury investigating criminal conduct overcame Nixon’s privilege. It is less settled which needs of Congress could overcome the privilege, but there is a very strong argument that the privilege should fall to the needs of an investigation that might lead to impeachment. Importantly, the privilege belongs to the president, who must authorize its assertion. And, the privilege extends only to the period of the presidency, not the campaign or the transition.

Insofar as we know, Trump has yet to assert formally executive privilege. Witnesses, however, acting on orders from the White House, have refused to answer questions on the basis that they want to preserve the president’s ability to do so in the future. That’s not the way it works. If the president does not assert the privilege, the witness appearing under compulsion must answer.

A witness under subpoena who refuses to answer questions without a valid claim of privilege can be held in contempt. Criminal contempt requires a referral to the U.S. Attorney for the District of Columbia for prosecution. The U.S. Attorney will not prosecute a witness for asserting executive privilege because the Justice Department will have opined already that the assertion is lawful. But, the House may sue for civil contempt. Only Steve Bannon — who managed to anger both Republicans and Democrats — has been subpoenaed by the committee, but there has been no move toward holding him in contempt.

The Republican majority’s refusal to use the committee’s investigative tools has created a sham process that too often allows for the appearance of action while allowing the White House to appear to be cooperating. The committee needs to convene public hearings, subpoena witnesses and hold reluctant witnesses in contempt. Maybe in 2019.

Bill Yeomans is the Senior Justice Fellow for Justice at Alliance for Justice. He previously taught constitutional law, civil rights, and legislation at American University Washington College of Law. He also served for 26 years in the Department of Justice, where he litigated cases involving voting rights and discrimination in employment, housing, and education, and prosecuted police officers and racially motivated violent offenders before assuming a series of management positions, including acting Assistant Attorney General. For three years, Bill served as Sen. Edward M. Kennedy’s chief counsel on the Senate Judiciary Committee, and has also held positions at AFJ and the American Constitution Society.