Transcript of a telephone conversation between U.S. President Donald Trump with Ukraine's president, Volodymyr Zelensky, held July 25, 2019.

In the ongoing Senate impeachment trial, the White House's defense of President Donald Trump hinges on keeping damning documents and witness testimony out of evidence. That is why, for the first time in our history, a president has defied every request for documents and witnesses from House impeachment investigators, and gone to extraordinary lengths to stop members of his own administration from testifying.

We have a party, in a trial, who controls the witnesses who know his true conduct, and that party is using that control to block important witnesses from testifying.

Our legal system saw this problem coming.

The "missing witness" rule, a longstanding common-law rule that the U.S. Supreme Court first discussed in 1893 in Graves v. United States, allows one party to obtain an adverse inference against the other for failure to produce a witness under that party's control with material information—an inference that the testimony would be harmful to them. Similar principles allow an adverse inference when a party refuses to turn over relevant documents. These rules prevent obstinate parties from abusing "costly and time consuming" court proceedings to subvert their legal duty to produce relevant evidence, as the U.S. Court of Appeals for the D.C. Circuit noted in International Union, United Automobile, Aerospace and Agricultural Implement Workers of America (UAW) v. National Labor Relations Board.

On Wednesday, I asked the House managers whether senators should draw an adverse inference regarding witnesses and documents withheld by the Trump administration. Witnesses like former national security adviser John Bolton, White House Chief of Staff Mick Mulvaney, Assistant to the President Robert Blair, and top Office of Management and Budget (OMB) official Michael Duffey have direct knowledge of the president's efforts to block aid to Ukraine. Documents at the Department of State, OMB and the Department of Defense corroborate the stories of career civil servants, who defied Trump's blockade and testified before the House.

Sometimes it is proper to exclude relevant evidence from a trial. Evidence may be unduly prejudicial or subject to a valid assertion of privilege. Parties can then file motions to compel or motions in limine. They make their case document by document and witness by witness.

However, a litigant cannot unilaterally decide what evidence is presented—and that is just what the White House attempted, and what my Republican colleagues in the Senate are ready to allow. The White House's refusal to produce these materials to Congress is particularly wrongful because they are releasing subpoenaed documents—often heavily redacted—through Freedom of Information Act requests.

There is a well-established procedure for the assertion of executive privilege; the president has never exercised it. Had he, it would have required privilege logs and triggered a process of negotiation and accommodation to balance the institutional interest the president has in confidential communications against Congress' institutional interest in conducting oversight. But here we have a White House saying, no witness, no documents, no way, no how.

This takes us to the White House counsel's defense against drawing an adverse inference: the argument that they interposed meritorious, good-faith objections and privileges. This does not pass scrutiny in my view. We heard arguments about absolute immunity—arguments that have been rejected by every court that has ruled on the issue. We heard claims that a vote of the full House on impeachment was required for standing committees to authorize subpoenas—claims that have no basis in the Constitution or the House rules, and overlook House oversight powers. Trump's lawyers claim we lack the evidence to impeach the president, while the president has bragged, "We have all the material. They don't have the material." They have faulted the House for not enforcing subpoenas in court, while arguing in court that courts are powerless to enforce them. The White House blockade does not evidence good faith and merit.

An added indication of the White House's intent is their argument that calling witnesses will cause the Senate impeachment trial to grind to a halt while the parties go to court to litigate issues of privilege. That argument has no basis. The Constitution mentions no such review, and the Supreme Court has held that courts have "no role" in a Senate impeachment, in Nixon v. United States. The Senate, with the assistance of the presiding officer, has always decided questions of privilege in impeachments, without parties resorting to the federal courts. There is no support for this assertion.

In the face of that brand of total obstruction, senators are well justified to turn to the missing witness rule and draw the adverse inference.

Alternatively, the Senate can solve this problem. We can issue subpoenas. We have an able chief justice sitting as our presiding officer to settle evidentiary disputes. But if my Republican colleagues decide a full and fair trial is not in the interest of the Senate, the law gives us a roadmap to fill in the resulting gaps: We can draw adverse inferences. In such circumstances, "[s]ilence then becomes evidence of the most convincing character," as Justice Harlan Stone noted in the high court's 1939 ruling, Interstate Circuit v. United States.

Sen. Sheldon Whitehouse represents Rhode Island in the U.S. Senate. A former Rhode Island attorney general and U.S. attorney, Whitehouse serves on the Senate Judiciary, Budget, Finance, and Environment and Public Works committees.