After dozens of House Republicans demanded access Wednesday to a secure facility in the Capitol where House Intelligence Committee Chairman Adam Schiff, D-Calif., was preparing to depose a Pentagon official, Democrats expressed outrage at the breach of protocol. “They’re doing this because this is what the guilty do,” said Rep. Eric Swalwell, D-Calif. “Innocent people cooperate with investigations. Innocent people follow the rules of the House.”

Well, people engaged in impartial investigations aimed at finding the truth don’t violate every precedent and standard of due process set during previous presidential impeachments.

Contrast today’s partisan inquiry with the Nixon impeachment. As American Enterprise Institute President Robert Doar has pointed out, the Nixon inquiry was a model of bipartisan cooperation. The Democratic chairman of the House Judiciary Committee, New Jersey Rep. Peter Rodino assembled a unified staff (including Doar’s father, John, a Republican whom Rodino appointed as special counsel). The full House voted on authorizing the inquiry. The minority was given joint subpoena power. The president’s counsel was allowed to be present during depositions, given access to all of the documents and materials presented to the committee, allowed to cross-examine witnesses, and even permitted to call witnesses of his own. Most important, the committee did not leak or release selective documents cherry-picked to make the president look bad.

The same was true during the Clinton impeachment inquiry. As former House Speaker Newt Gingrich explained in a recent interview, Republicans “adopted every single rule that Rodino had used in 1973.” Yet today, Rodino’s party is systematically undermining every principle of fairness and due process he put in place in 1973.

Take this week’s testimony by acting Ambassador William Taylor, who alleged that President Trump made U.S. aid contingent on “investigations.” He was deposed inside a Sensitive Compartmented Information Facility in the Capitol, a room that is designed to protect the government’s most highly classified information. Cellphones are not permitted inside such a facility. Yet somehow what appear to be cellphone photos of his prepared statement were leaked to the news media.

But the full transcript of his deposition – including his answers to questions from Republicans challenging his accusations – remains under lock and key in that ultra-secure facility. The president’s counsel is not allowed to see it, much less be present at the deposition to cross-examine the witness. So, Democrats are leaking derogatory information about the president, while restricting public access to potentially exculpatory information, all while denying him the right to see or challenge testimony against him.

Moreover, they are abusing the system to do it. One of the charges Democrats have leveled against Trump is that the White House improperly put the transcript of his call with the Ukrainian president on a special server used to protect highly classified information. Yet Democrats are doing the very same thing, conducting impeachment depositions inside a Sensitive Compartmented Information Facility, improperly using a classified system to restrict access to nonclassified information not just to the public but also to members of Congress. Talk about hypocrisy.

Let’s be clear: There is nothing wrong with holding hearings behind closed doors as long as there is due process. But secrecy and fairness go hand in hand. One without the other is corrupt.

The partisan nature of the Democrats’ inquiry will backfire in a number of ways. For one thing, it allows Republicans to make the case to the American people that the process is unfair. If the facts are on the Democrats’ side, then theyy have nothing to fear from transparency and due process. Second, their partisan behavior has given the president justification for refusing to cooperate with the investigation, just as President Dwight Eisenhower refused to cooperate with the Army-McCarthy hearings in 1954. And finally, it has made it easier for congressional Republicans to rally around the president. Right now, Republicans are more torn about Trump’s Syria policy than they are about his impeachment inquiry. By failing to show even a modicum of fairness, Democrats have turned impeachment into a game of shirts vs. skins.

The Democrats’ conduct shows that they are not serious, and that the entire impeachment inquiry is a blatantly political exercise. Given the Constitution’s requirement of a supermajority in the Senate to remove the president, it is impossible for one party to remove the president of another party from office without buy-in from the other side. Yet Democrats are making no effort to win over Republicans, much less make a vote against impeachment difficult. And that means they’ll have a hard time getting buy-in from the American people.

Washington Post columnist Marc A. Thiessen is a fellow at the American Enterprise Institute and former chief speechwriter for President George W. Bush.

Twitter: marcthiessen