Photo by Sipa via AP Images / Former U.S. ambassador to Ukraine Marie Yovanovitch arrives Friday to testify at a House Intelligence Committee impeachment hearing of President Donald Trump on Capitol Hill in Washington.

The testimony in this week's impeachment hearings before the House Intelligence Committee has been commanding and damning toward President Donald Trump. Without question, however, the president himself gave the most damaging testimony — against himself.

First he has continued to provided silent testimony by refusing to provide requested documents or witnesses to the congressional committees investigating a matter of which he says he's innocent. Then on Friday, Trump penned an intimidating tweet to witness Marie Yovanovitch, the former ambassador to Ukraine, in real time as she was testifying.

Trump named Yovanovitch in the tweet, but she wasn't the only intended recipient of his heavy-thumbed threat. On the contrary, every past and future witness now clearly knows their pictures, too, are on posters in Trump's head.

In the hearing, Yovanovitch had just been answering questions about how previous tweets and statements by Trump, Donald Trump Jr. and Rudy Giuliani had made her feel — threatened. She became especially concerned, she said, when she read the transcript of the president's July 25 phone call with the new president of Ukraine. In that call, the president called her "bad news" and said "she's going to go through some things."

"It was a terrible moment," she told the House Intelligence Committee in Friday's public hearing. "A person who saw me actually reading the transcript said that the color drained from my face. I think I even had a physical reaction. I think, you know, even now, words kind of fail me."

(Read more: Ousted ambassador testifies ouster helped 'shady interests')

She was shocked, appalled and devastated, she said. "Devastated that the president of the United States would talk about any ambassador like that to a foreign head of state — and it was me. I mean, I couldn't believe it. ... It sounded like a threat."

So what did the president do even as Yovanovitch spoke those words aloud to the American public?

He did it again.

"Everywhere Marie Yovanovitch went turned bad," Trump wrote on Twitter. "She started off in Somalia, how did that go? Then fast forward to Ukraine, where the new Ukrainian President spoke unfavorably about her in my second phone call with him. It is a U.S. President's absolute right to appoint ambassadors."

The chairman of the committee, Rep. Adam B. Schiff, D-California, took advantage of the president's real-time rejoinder to read it aloud and ask Yovanovitch what she thought of it.

Looking uncomfortable, she responded: "It's very intimidating. I can't speak to what the president is trying to do, but the effect is to be intimidating."

Schiff had no trouble speaking to the president's effort.

"Some of us here take witness intimidation very, very seriously," he said.

(Read more: Takeaways from Day 2 of House impeachment public hearings)

Unless you've been living in a cave without electricity or cellphone signal for the past six months, you know that Friday's and Wednesday's impeachment hearings were prompted by a legal and formal whistleblower complaint last August saying that White House officials believed they had witnessed Trump abuse his power for political gain. The complaint said Trump — along with an irregular and unofficial foreign policy effort led by Rudy Giuliani — pressured the new president of Ukraine to investigate former Vice President Joe Biden, a potentially strong opponent of Trump in the 2020 election, for Trump's own political gain. Trump also asked that Ukraine "find" evidence that would absolve Russia in our election meddling.

All this occurred while Trump had placed a hold on U.S. aid to Ukraine — aid the country desperately needed to fight off Russian aggression. And Ukraine knew Trump was withholding the aid. It was quid pro quo. Or in the words of Democrats, bribery and extortion — the makings of impeachable behavior.

The whistleblower's complaint specifically mentioned the president's second phone call with new Ukrainian President Volodymyr Zelenskyy. When the White House a few days later released a partial and rough transcript of that call, the read-out bore out the allegations made by the whistleblower.

Trump, however, denied it all, saying the call was "perfect."

So perfect that it has brought us to this point: Impeachment hearings.

But in typical Trump reality TV fashion, he just keeps denying. He's even given to rally attendees — at least those staged behind him — T-shirts emblazoned with "Read the transcript."

(Read more: Trump says impeachment probe has been 'very hard' on family)

Perhaps that was upstaging for Friday when, just in time for the testimony of Yovanovitch, the White House released what it said was the transcript of the first call, on April 21, between Trump and Zelenskyy. This one — devoid of the ellipses that dotted the rough summary of the July 25 document — is singularly unremarkable. Perhaps it's the one Trump thinks was released the first time around — the "perfect" one.

As for timing, the second transcript release (of the April call) was so convenient that Trump apologist Rep. Devin Nunes, the top Republican on the impeachment inquiry committee, already had it in a nice folder and read it aloud as part of his opening statement Friday.

As for Yovanovitch, she was merely an ambassador carrying a normal "no-corruption" U.S. foreign policy message in the country of an ally, but she was in the way of what Trump and Giuliani wanted.

Yet, during the five-hour hearing, Democrats and Republicans alike praised her, and as her testimony ended, she received a standing ovation from the public in the hearing room.

That ovation should be taken as a vote of confidence, not just for her, but also for the witnesses who preceded her — diplomats George Kent and William Taylor — and all the ones who will be brave enough to follow.