The past two weeks of devastating testimony in the House Intelligence Committee confirmed that Trump demanded that Ukrainian President Zelensky announce investigations of Joe and Hunter Biden and of the 2016 election. Only then would he agree to an Oval Office visit and release $391 million in military assistance Congress had already approved. The powerful testimony of a dozen witnesses left the facts indisputable: Trump used the power of his office to extort political favors from a foreign leader. For his actions, he should be impeached, convicted, and removed from office.

Beyond nailing down the basic facts of the extortion scheme, the testimony established that the effort lasted for months and involved not just Rudy Giuliani and his associates, but numerous actors at the top levels of Trump’s Administration. Ambassador Gordon Sondland, named, among others, Vice President Mike Pence, Secretary of State Mike Pompeo, acting White House Chief of Staff Mick Mulvaney, former National Security Advisor John Bolton, and Energy Secretary Rick Perry as “in the loop” on the scheme. We didn’t learn as much as we should have about their involvement because all have bowed to Trump’s instructions to refuse all cooperation with the impeachment investigation.

The widening field of participants fuels two important questions: 1) how soon to wrap up the investigation, and 2) why there isn’t a parallel criminal investigation of Trump’s collaborators.

1) The first question has been pending since the start of the inquiry. Driven in large measure by the election calendar, the House majority has felt obliged to shape a clean narrative that can produce a prompt vote on articles of impeachment, followed by an expeditious trial in the Senate. That schedule would prevent impeachment from running into and drowning out the Democratic presidential primaries and allow senators up for reelection to hit the campaign trail.

The argument for extending the investigation, however, is stronger. It is clear that the case put on in the Committee so far — regardless how overwhelming — has yet to change public opinion. That has allowed Republicans in both the House and Senate to continue their defense of Trump without paying a political price. The Senate will almost certainly acquit Trump based on the current record, even with the addition of necessary articles of impeachment alleging obstruction of justice and contempt of Congress. Any responsible prosecutor, knowing that a jury will almost certainly not find a defendant guilty on the existing evidence, but knowing that further investigation likely will produce substantially more evidence, would continue the investigation.

While it may be that there is no quantum of evidence that would crack the fact-resistant Republican wall that protects Trump, the odds of making a dent would increase if even more key players submitted to questioning and produced relevant documents. Obtaining testimony and documents might require time-consuming court intervention, but that process could accelerate as courts inevitably reject Trump’s absurd claim of absolute immunity. Internal administration squabbling will motivate some to talk. In addition, more whistleblowers could emerge and more leaks might spring. A prolonged process will keep Trump’s misdeeds in the public spotlight, doubtless provoking him to lash out in ways that clarify his culpability.

While the House must be careful not to overload the system, it should remember that it is speaking to history. Any misdeeds of Trump that are apparent and go unaddressed become acceptable.

Finally, if the Senate acquits Trump quickly, he will have more time to corrupt the upcoming election. Just as he picked up the phone to call President Zelensky the day after Mueller’s poorly received testimony, he will feel similarly unleashed after a Senate acquittal. He solicited help from Russia and Ukraine. If unchecked, he will surely try again. We can hope that he will feel constrained so long as his conduct is under intense scrutiny and impeachment remains in play.

2) Criminal law has yet to play a substantial role in the Ukraine affair. By contrast, the Nixon and Clinton impeachment efforts and the congressional Iran/Contra investigation were accompanied by criminal investigations that developed evidence and gave witnesses powerful incentives to cooperate. In the normal course, the growing evidence that Trump orchestrated a bribery, extortion, and campaign finance conspiracy that looped in a significant number of officials would result in a federal criminal investigation. The bar for launching an investigation is relatively low. Investigators need only a “reasonable indication” that a crime has been or will be committed. That’s far lower than a preponderance of proof and much below the proof beyond a reasonable doubt needed to convict.

Attorney General Barr, however, remains determined to protect Trump. He continues to pursue discredited conspiracy theories about the 2016 election. He is deeply immersed in the muck of the Ukraine scandal, having been mentioned repeatedly by Trump as his contact in the Zelensky call. He also attempted to block the whistleblower complaint from reaching Congress and refused even to open an investigation into the Inspector General’s criminal referral based on the whistleblower’s complaint. Not only will Barr resist opening a frontal investigation regarding Ukraine, DOJ will continue to argue that witnesses need not testify. It is not clear even that DOJ will prosecute witnesses who lie to Congress.

 The Special Counsel appointment authority exists precisely for these circumstances – where the Department of Justice is conflicted, particularly in a matter involving high ranking government officials, and the public interest demands a federal criminal inquiry. Barr should recuse himself and allow the appointment of a special counsel. He will not.

The U.S. Attorney’s office for the Southern District of New York, however, is approaching through a side door. It has charged Rudy Giuliani’s two associates with campaign finance-related violations. Reports of recent subpoenas suggest the office is expanding its investigation to include Giuliani’s Ukraine-related conduct. If it does, the investigation necessarily will reach public officials who participated with Giuliani in Trump’s scheme. At that point, all eyes will be on Barr.

The current posture of the Department of Justice is a powerful reminder of the price we are paying for Trump’s trampling of the independence of the office of the Attorney General. The investigative efforts of Congress, therefore, become all the more essential. They should not be truncated.

Bill Yeomans is the Senior Justice Fellow at Alliance for Justice. He currently serves as Lecturer in Law at Columbia Law School, and 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.