Wednesday’s congressional testimony by Michael Cohen, former personal attorney for President Donald Trump, proved an extraordinary moment in modern American history. Cohen, employed by Trump for more than a decade, privy to the inner workings of his organization, while under oath before a House committee, called the president a con man, a racist and a cheat, named names and provided documents.

Cohen is himself a disgraced figure, convicted of lying to Congress and evading his taxes, disbarred from his profession and headed to prison. That calls into question the veracity of whatever statements he makes.

But as serious as Cohen’s transgressions are, that does not mean he should not be heard, as Republicans on the committee seemed to believe. Any investigator knows that in attempting to gather evidence of illegal activity, those with the most information often will not be without blemish. As Rep. Gerald Connolly, D-Mass., said during the hearing, such a standard would “discredit every single criminal trial in the history of the United States. … This Congress historically has relied on all kinds of shady figures who turn.”

Congress’ job — and it’s a difficult one — is to use all of the powers at its disposal to determine the facts about the critical question now facing this nation: Did Trump commit illegal actions as a candidate or officeholder?

Cohen is only as useful as the hard evidence he is able to produce or have corroborated. His testimony produced ample leads, so that Congress need not rely exclusively on his word. He offered canceled checks from his personal account — including one signed by Trump — that he said were reimbursement for money Cohen paid to cover up an affair — something Trump is on record as having denied and which would violate campaign finance laws.

The self-described “fixer” said he has recorded phone calls and “boxes” of evidence already reviewed by the FBI and now back in his possession. He submitted several years of Trump’s financial documents sent to Deutsche Bank in which the attorney said Trump inflated assets to obtain loans. Cohen testified that Trump instructed him to threaten individuals and institutions 500 times over the years, including Trump’s own high school and colleges to prevent them from releasing his grades and scores. Cohen said Trump directed him to lie to Congress, and that Trump knew in advance of the 2016 WikiLeaks stolen e-mail dump. He said Trump’s lawyers reviewed and edited the false statement Cohen gave Congress in 2017 about a Trump building deal with Moscow.

The American public should consider itself fortunate that after two years of a Congress that failed miserably to uphold its watchdog role, some facts are beginning to come to light. Much more must be done, including protecting the Mueller investigation and ensuring that its findings make their way to Congress and obtaining Trump’s tax returns, to shed light on his dealings.

The presidency is a sacred trust. Not every officeholder will live up to its demands and standards. But when there is reasonable suspicion of wrongdoing, transgressions should not be papered over out of tribalism. For two years, the nation has been awash in a cloud of lies and spin, norm-trashing and constant chaos, to the point where many unfortunately have become inured. That is a dangerous place for a country built on the rule of law.

The only corrective is to replace heat with light and lies with facts.

Republicans should be eager to return to that standard for their own sake and that of their party. If they can factually disprove Cohen’s allegations, that would discredit him far more than just restating his past wrongdoing.

Cohen in his testimony offered what may be a prophetic warning about misplaced loyalty. “I did the same thing that you’re doing now for 10 years,” he told Republicans at Wednesday’s hearing. “I protected Mr. Trump for 10 years … Look what’s happened to me.”