Last week, Judge Arthur F Engoron of the supreme court of the state of New York ruled that former president Trump, his son Donald Trump Jr, and his daughter Ivanka Trump must produce documents and testify under oath in a civil investigation into their valuations of their business assets, complying with a subpoena New York attorney general Letitia James issued for their testimony in December.

The Trumps can invoke their rights under the fifth amendment to the constitution not to incriminate themselves. This is what Eric Trump did more than 500 times in October 2020, when he testified before members of the attorney general’s office. In a civil trial, however, invoking the fifth can be interpreted negatively.

After the decision, James tweeted: “No one is above the law.”

The Trumps intend to appeal.

The arguments in last week’s hearing raised a troubling point. Trump sued Attorney General James last December, alleging that “[h]er mission is guided solely by political animus and a desire to harass, intimidate, and retaliate against a private citizen who she views as a political opponent.” In the hearing, Trump’s lawyers continually portrayed James’s investigation not as a valid exercise in protecting the rule of law, but as a political attack on Trump. His lawyers argued that James’s investigation is “selective prosecution” and is “unconstitutional”, and that she is pursuing the case only to hurt the former president before the 2024 election.

The judge rejected these claims, pointing out, among other things, that none of the 600 or more documents in the case refer to Trump’s politics; they focus on his financial practices. “In the final analysis,” the judge wrote, “a State Attorney General commences investigating a business entity, uncovers copious evidence of possible financial fraud, and wants to question, under oath, several of the entities’ principals, including its namesake. She has the clear right to do so.”

Trump’s attempt to portray as political any legal reckoning for him for potential wrongdoing with regard to his finances dovetails with the attempt of Trump and his loyalists to paint the House Select Committee to Investigate the January 6th Attack on the US Capitol as partisan.

Repeatedly, they have called the committee “illegitimate” because Democratic House speaker Nancy Pelosi did not put on it the members Republican House minority leader Kevin McCarthy nominated. She had the right to review his nominations, and she rejected Republican representative Jim Jordan, who has now been implicated in the events of the day, and Republican representative Jim Banks, who had attacked the committee as a partisan exercise “solely to malign conservatives and to justify the left’s authoritarian agenda”. He announced that he would use his place on the committee to investigate the protests of summer 2020 instead of the events of January 6.

After rejecting Jordan and Banks, Pelosi asked McCarthy to nominate others in their place, but instead he withdrew all the Republicans from the committee. At that point, she invited Republican representatives Liz Cheney and Adam Kinzinger to join the committee. Although Trump Republicans are portraying Cheney as a turncoat, she voted with Trump’s agenda 92.9% of the time. Kinzinger voted with Trump 90.2% of the time.

Nonetheless, Trump loyalists dismiss the two Republicans on the committee and claim the committee is partisan. Some are talking about turning the committee against the Democrats as soon as the House is back in their hands. Former speaker of the House Newt Gingrich told the Fox News Channel: “I think when you have a Republican Congress, this is all going to come crashing down, and the wolves are going to find out that they’re now sheep and they’re the ones who are in fact, I think, fac[ing] a real risk of jail for the kinds of laws they’re breaking.”

Democratic representative Jamie Raskin, a constitutional law professor and member of the January 6th committee, noted: “That’s the language of authoritarianism.”

Meanwhile, in an unusual move against an incumbent of his own party, House minority leader McCarthy has endorsed the Trump-backed primary opponent of Representative Liz Cheney, who is the vice-chair of the January 6th committee. Trump and his allies are working this same game, pressing Wyoming’s Republican governor, Mark Gordon, to back a bill that would change state law to prevent Democrats from voting in the Republican primary, thus likely giving a primary victory to Cheney’s opponent. Although Cheney has said she will not encourage Democrats to support her in the primary, the Trump loyalists are prepared to change the law to put a Trump ally in her place.

Last week, Trump lashed out about the legal developments of the past few days. He insisted that the suggestion by special counsel John Durham that operatives for Hillary Clinton spied on Trump as president – a suggestion Durham backed away from today –and Judge Engoron’s decision today were entirely partisan.

Trump claimed that Clinton, “one of the most corrupt politicians ever to run for president, can break into the White House, my apartment, buildings I own, and my campaign – in other words, she can spy on a Presidential candidate and ultimately the president of the United States – and the now totally discredited Fake News Media does everything they can not to talk about it.” (These allegations are false, of course.) On the other hand, he said, attorney general James is selectively prosecuting him and his family.

“[T]he Radical Left Democrats don’t want [him] to run again,” he wrote, and their targeting of him “represents an unconstitutional attack on our Country… a continuation of the greatest Witch Hunt in history.” Finally, he said, “I can’t get a fair hearing in New York because of the hatred of me by Judges and the judiciary. It is not possible.”

There is a dangerous theme running through these stories, as well as Trump’s attack on Fulton county district attorney, Fani Willis, who is investigating Trump’s attempt to pressure Georgia secretary of state Brad Raffensperger to overturn the results of the 2020 election in Georgia and award that state’s electoral votes to him, rather than to the actual winner, Joe Biden. Earlier this month, Trump told attendees at a rally in Texas that he hoped they would take to the streets with “the biggest protest we have ever had”, if “these radical, vicious racist prosecutors do anything wrong or illegal”.

Trump and his loyalists are setting up the idea that any attempt to hold Trump and his allies accountable for illegal activities – including the attempt to overturn the 2020 election and thereby destroy our democracy – is a partisan attack. While that argument will undermine the rule of law, there is a twist to it: if Republicans can convince their voters that Democrats have engaged in partisan prosecutions of Trump and his allies, the Republicans can justify partisan prosecutions of Democrats as soon as they get the opportunity, just as Gingrich suggested. If this rhetoric works, Trump can undercut legitimate prosecutions, while Democrats will become fair game for partisan prosecutors.

This is indeed, as Representative Raskin said, the language of authoritarianism.

• Heather Cox Richardson is an American historian and professor of history at Boston College. She is the author of Letters from an American, a daily newsletter about American politics and history