As any lawyer knows, you’re not supposed to cross-examine a witness by asking questions you don’t know the answer to. But that happened over and over again with Republicans at Thursday’s impeachment hearing, and it had predictably ugly consequences for the GOP.

Repeatedly, former White House aide Fiona Hill and Ukraine diplomat David Holmes confidently challenged the premises of the lines of questioning and arguments offered by the Republicans on the House Intelligence Committee. Unlike previous witnesses who were happy just to recite facts and their recollections, Hill and Holmes anticipated when the GOP members were going in directions they felt were misleading, and they assertively corrected the record.

It became clear, as the hearing went on, why the majority Democrats saved these two witnesses for the final planned hearing of the impeachment inquiry.

The most telling example came when the committee’s top Republican, Rep. Devin Nunes (Calif.), tried to establish the premise that the “black ledger” Ukraine shared on former Trump campaign chairman Paul Manafort wasn’t credible.

Holmes declined to grant that premise, though, and he seemed to have done his homework:

NUNES: And the black ledger — is that seen as credible information?
HOLMES: Yes.
NUNES: The black ledger is credible?
HOLMES: Yes.
NUNES: [Former special counsel Robert S. Mueller III] Bob Mueller did not find it credible. Do you dispute what Bob Mueller’s findings were? They didn’t use it in the prosecution or in the report.
HOLMES: I’m not aware that Bob Mueller did not find it credible. I think it was evidence in other criminal proceedings. Its credibility was not questioned in those proceedings. But I’m not an expert on it.

It was the kind of premise that your average witness — or even one just not terribly interested in rocking the boat — would probably have let slide.

Later, GOP counsel Stephen Castor asked Holmes about a review that was conducted of how much European allies gave in aid to Ukraine. Castor’s idea was apparently to suggest Trump was actually concerned about burden-sharing when he withheld military aid, rather than political leverage for investigations that could help him politically.

But Holmes interjected. He made a point to note that the review happened after — and he emphasized that word — the Ukraine money was held up. Then he described the findings, which he labeled “illuminating."

“The United States has provided combined civilian and military assistance to Ukraine since 2014 of about $3 billion plus. ... Three $1 billion loan guarantees — those get paid back, largely,” Holmes said. “So just over $3 billion. The Europeans, at the level of the European Union plus the member states combined since 2014, my understanding have provided a combined $12 billion to Ukraine.”

The retort was clear: Castor’s argument was pretty nonsensical.

When questioning Hill, Castor tried to establish some background by asking questions that would usually elicit very brief responses. But she often provided very detailed responses that interrupted the arc of his argument — and sometimes took things in a much different direction.

A key one came when Castor seemed to be trying to poke holes in Sondland’s damaging testimony Wednesday. He asked about disputes between the two of them — which have occasionally broken out publicly in recent weeks.

But Hill turned it into an answer about how correct Sondland’s testimony was, after reviewing it closely.

“Now I actually realize, having listened to his deposition, that he was absolutely right — that he wasn’t coordinating with us because we weren’t doing the same thing that he was doing,” Hill said.

She added: “Because he was being involved in a domestic political errand. And we were being involved in national security, foreign policy. And those two things had just diverged. So he was correct. And I had not put my finger on that at the moment, but I was irritated with him and angry with him that he wasn’t fully coordinating. And I did say to him, ‘Ambassador Sondland — Gordon — I think this is all going to blow up.’ And here we are."

At another point, Castor suggested to Hill that the “three amigos” — Sondland, former special envoy to Ukraine Kurt Volker and Energy Secretary Rick Perry — had little contact with Trump’s personal lawyer Rudolph W. Giuliani before July 19.

Hill, though, had apparently extensively reviewed her fellow witnesses’ testimony, and suggested that was wrong:

CASTOR: Just for sake of a timeline, I think as of July 19, they hadn’t even engaged with Rudy Giuliani. And I don’t believe that happened until a little bit later. So you believe by July 19, they were already engaged in those types of activities?
HILL: We had already had a discussion with Kurt Volker, which was in the depositions of his assistant, Chris Anderson, that indicated that he had met with Rudy Giuliani at this point. And Ambassador Sondland made comments about meeting with Giuliani. And as we know in the May 23 meeting they had been instructed to meet with Giuliani. They gave us every impression that they were meeting with Rudy Giuliani at this point, and Rudy Giuliani was also saying on the television and indeed has said subsequently that he was closely coordinating with the State Department. So it was my belief that they were meeting with him.

Anderson did indeed testify that Volker told him around the “late spring” that he had previously been in touch with Giuliani. He said he believed he learned that even before Trump directed the “three amigos” to “talk to Rudy” on May 23, though he couldn’t be sure.

But unless Anderson’s timeline was way off, that would put the contacts well before the July 19 date Castor suggested. It wasn’t perhaps the worst GOP moment in the hearing, but it had plenty of even-worse company.