Finally, a smoking pun. A simple play on words told us everything about the impeachment inquiry, the current mindset in Congress and the state of the nation.

The witness Pamela Karlan cracked a joke that delighted liberals and infuriated conservatives. Or rather, it delighted conservatives because it gave them a talking point to whip up outrage.

The afternoon session of the House judiciary committee hearing on the constitutional framework for impeachment had just begun when the Democratic congresswoman Sheila Jackson Lee posed the question: “What comparisons can we make between kings that the framers were afraid of and the president’s conduct today?”

Karlan, a Stanford Law School professor, replied: “Kings could do no wrong because the king’s word was law. Contrary to what President Trump has said, article two [of the constitution] does not give him the power to do anything he wants.

“I will give you one example that shows the difference between him and a king, which is: the constitution says there can be no titles of nobility. While the president can name his son Barron, he can’t make him a baron.”

Jackson Lee smiled and there was laughter in the big and ornate committee room, where two carved eagles look down under the words “E pluribus unum” (out of many, one) and a dozen uniformed Capitol police lent an air of a courtroom drama. Karlan’s point echoed Judge Ketanji Brown Jackson’s recent opinion, cited at Wednesday’s hearing, that “the primary takeaway from the past 250 years of recorded American history is that presidents are not kings”.

But could we forgive the pun? Not when the president’s son, tall but only 13 years of age, was involved. Republicans’s well-oiled fury machine clicked straight into gear. Stephanie Grisham, the White House press secretary, tweeted: “Classless move by a Democratic ‘witness’. Prof Karlan uses a teenage boy who has nothing to do with this joke of a hearing (and deserves privacy) as a punchline.”

The Trump 2020 election campaign demanded Karlan personally apologise to the president and first lady. Back in the room, the Trump loyalist Matt Gaetz expressed righteous indignation. “When you invoke the president’s son’s name here, when you try to make a little joke out of referencing Barron Trump, that does not lend credibility to your argument,” he told Karlan.

Like Jim Jordan and Elise Stefanik in the intelligence committee hearings, Gaetz would have known that clip has plenty of potential for replays on Fox News and rightwing social media, bashing the left as vengeful and in the throes of “Trump derangement syndrome”.

As the clock ticked past half-five, the hearing learned, with an audible gasp, that Melania Trump herself had weighed in, tweeting: “A minor child deserves privacy and should be kept out of politics. Pamela Karlan, you should be ashamed of your very angry and obviously biased public pandering, and using a child to do it.”

Karlan apologised. “It was wrong of me to do that,” she told the hearing. “I regret having said that.”

The division over this pun – a laugh line to some, evidence of liberal sneering to others – cut to the chase of yet another hopelessly polarised hearing. Facts mattered less than being on the winning team. It made one wonder whether Americans don’t even laugh at the same jokes any more.

Three of the witnesses, including Karlan, had been called by Democrats to testify that the evidence gathered regarding Trump’s dealings with Ukraine meets the historical definition of impeachment. The other witness had been called by Republicans. Few Democratic or Republican politicians put a question to a witness from the other side.

Democrats got plenty of ammunition. Representative Steve Cohen laid out an ABC – Abuse of power, Betrayal of the national interest and Corruption of elections – and asked if Trump had achieved the trifecta. “Yes,” replied all three Democratic witnesses. Michael Gerhardt, a University of North Carolina law professor, said: “I just want to stress that if what we’re talking about is not impeachable, then nothing is impeachable.”

But their opponents worked tirelessly to argue that their witnesses were partisan ivory tower-dwellers and therefore ignorable in this “sham” and “farce”.

The Republican witness was Jonathan Turley, who was somewhat measured, opining that Trump’s phone call with the Ukrainian president “was anything but perfect”. But the George Washington University law professor said: “One can oppose President Trump’s policies or actions but still conclude that the current legal case for impeachment is not just woefully inadequate, but in some respects dangerous.”

There were also some structural problems for Democrats in the all-important court of public opinion. At hearings like Wednesday’s, they have to take turns with Republicans, which creates an impression of equivalence: first let’s put the case for the world being round, now let’s hear the case that it’s flat.

So before some empty seats in the press and public galleries, members continued to talk past each other.

For those still watching at home, the alternatives were sleep or, after the TV newsman Howard Beale in the film Network, to cry out: “I’m as mad as hell, and I’m not going to take this any more!”

Turley had an answer for that too. “I get it. You’re mad,” he said. “The president’s mad. My Republican friends are mad. My Democratic friends are mad. My wife is mad. My kids are mad. Even my dog seems mad. And Luna’s a goldendoodle, and they don’t get mad. So we’re all mad.”