The context of Trump’s personal lawyer Michael Cohen’s testimony before the House oversight committee on Wednesday was more important than its content. Cohen established what was already widely suspected: that the president is accused of committing crimes. But the hearing did something else, too: it revealed to a television audience the utter bankruptcy of Trump’s Republican party at the very moment that Republican senators must choose whether or not to uphold Trump’s extraordinary assumption of power under his 15 February declaration of emergency.

Until now, it has been difficult to know what was really going on in the Trump White House. Special counsel Robert Mueller, who is charged with investigating Russian interference in the 2016 election but who has uncovered a number of other potential crimes, operates in impressive silence. The grand jury indictments that have produced guilty pleas from Trump’s former campaign chair, his national security adviser, and a slew of other operatives are often confusing.

The Republicans who controlled Congress in the first two years of Trump’s administration obscured the machinations of their leadership even as evidence of criminal activity mounted. They kept the public in the dark by refusing to hold hearings, ignoring witnesses, and producing narrow or incomplete reports denying wrongdoing, all while Republican operatives assured their base that Trump was the most maligned president in history. Without public testimony, it was possible for Republican party leaders to maintain that a defense of Trump was principled conservatism.

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But now, Democrats control the House of Representatives, and Cohen is the first witness they have called to testify to the criminality of the Trump White House. From the night before the public hearing, when Florida representative Matt Gaetz threatened Cohen on Twitter, to the minutes before the hearing, when Mark Meadows of North Carolina tried to delay the hearing, to the beginning of the session when the ranking Republican member, Jim Jordan, came out of the gates accusing the Democrats of running a partisan investigation, it was clear the Republican party did not want the public to hear what Cohen had to say.

Play Video 1:28 Trump loyalists will 'suffer same consequences I’m suffering', says Cohen – video

This is understandable, since over the course of his testimony, the picture Cohen painted was of a president who thinks and acts like a crime boss.

According to Cohen, President Trump knew in advance about the WikiLeaks dump of the Democratic National Committee emails stolen by Russia, paid hush money to Stormy Daniels, urged Cohen to lie to Congress, and even, in an extraordinary exchange that will certainly stick with listeners, ordered Cohen to threaten as many as 500 people.

Strikingly, Republican members of the House committee did not defend the president against Cohen’s charges. They arrived at the hearing unprepared, badly mismanaged their time and their questioning, and seemed to expect the chair to indulge them. When Democrat Elijah Cummings did not, they simply called Cohen a liar and worked to derail the proceedings by entering tweets into the record, including a tweet by Fox personality Bo Deitl, starting a ruckus over whether or not Trump is a racist, and, astonishingly, displaying a poster with Cohen’s face that read: Liar, Liar, Pants on Fire. Only Republican member Justin Amash, a representative from Michigan, treated the event with gravity.

This was political theater, but with the Democrats in control, the Republican party had lost control of the script. They acted not like a political party, but like a cult whose members had lost all intellectual coherence and professionalism and had retreated into sycophantic support for a strongman.

The timing of this display is important. On 15 February, Trump made an unprecedented power grab by issuing an emergency declaration giving him power to build a wall on America’s southern border, despite Congress rejecting his demand.

On Tuesday, the House of Representatives passed a resolution overturning Trump’s declaration of emergency, with 13 Republicans breaking with Trump to join the Democratic majority. The resolution is now at the Senate, where Republicans barely hold the majority, and where each senator’s vote will become a test of loyalty to the president.

In his final statement, Cohen laid out the stakes very clearly: Trump might not cede power if defeated in 2020. Will Senate Republicans finally check the career of a president, and a party, that has so thoroughly demonstrated its depravity?

• ​Heather Cox Richardson is professor of ​history at Boston College and co-​host of NPR’s politics and history podcast Freak Out and Carry On