As Marie Yovanovitch testifies, the president is tweeting a defence of his foreign policy.

"I have done FAR more for Ukraine than O[bama]."

At the time the call to leave her post came in, she was hosting an event honouring an anti-corruption activist in Ukraine, Yovanovitch says.

That activist later died from an acid attack, she says.

Yovanovitch says her boss told her there were "concerns regarding her security" that forced her to leave.

The ex-US ambassador to Ukraine said she found it "not surprising" that anti-corruption efforts were resisted by "Ukrainians who preferred to play by the old corrupt rules" and "sought to remove me".

But, she said, "what continues to amaze me is that they found Americans willing to partner with them".

Image source, Win McNamee/Getty Images

"If you fight corruption you're going to piss off some corrupt people," says Schiff, who then asks if she has angered corrupt Ukrainian prosecutors.

"Yes," she replies.

Schiff says she was "smeared out of her post with the participation and acquiescence of the president of the United States".

In addition to today's witness, Marie Yovanovitch, there are a few other faces you should know.

The top lawmakers:

And their counsel:

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Democratic Chairman Adam Schiff has begun 45 minutes of questions, starting with a question about why fighting corruption in Ukraine was a US priority.

"Because corruption was undermining the integrity of the government system," she says, adding that is a "Soviet legacy".

Image source, Win McNamee/Getty Images

Yovanovitch again stressed her "grave concerns about the degradation of the foreign service", as she did during her earlier closed-door deposition.

She says the state department's leadership failed "to push back as foreign and corrupt interests apparently hijacked our Ukraine policy".

"I remain disappointed that the department’s leadership and others have declined to acknowledge that the attacks against me and others are dangerously wrong."

The department's leader? Trump loyalist Secretary of State Mike Pompeo - who has called Democratic subpoenas of his staff "bullying" tactics.

More on Pompeo here

Yovanovitch says "the smear campaign against me entered a new public phase" in March 2019, shortly after she agreed to extend her Ukraine role until 2020.

Only weeks after the extension, she was called back to Washington for security reasons, she was told.

When she returned, her boss told her there had a been a "concerted effort against her" led by Trump.

Yovanovitch tells lawmakers: "Individuals who apparently felt stymied by our efforts to promote stated US policy against corruption - that is, to do the mission - were able to successfully conduct a campaign of disinformation against a sitting ambassador, using unofficial back channels."

These people, she says, shared "baseless allegations" with Trump and convinced him to oust her - despite the fact the state department knew these claims were false.

Image source, Drew Angerer/Getty Image

Yovanovitch says the claim - made by some Republicans - that she disseminated a "Do Not Prosecute" list was "a fabrication".

She would never take any step to help any US political campaign, as that is not the role of a foreign service diplomat, she said.

"I have never met Hunter Biden. Nor have I had any direct or indirect conversations with him," she added.

Trump's effort to have Ukraine investigate Hunter Biden, who worked for a Ukrainian energy firm, is at the centre of the Democrats abuse of power inquiry.

Yovanovitch mentioned that she never directed Yuriy Lutsenko about a "do not prosecute" list. So who is he?

Lutsenko is the former prosecutor-general of Ukraine.

In September, he told the BBC's Jonah Fisher that his country had no jurisdiction to investigate Joe Biden's son, Hunter.

Image source, NICHOLAS KAMM/AFP via Getty Images

During Wednesday's testimony, representatives for the president said he was hard at work in the Oval Office, avoiding the "sham hearing".

Still, the president fired off 34 tweets and retweets on Day 1 of the Democrat-led probe, dismissing it as a "phony showtrial".

By 9:00 local time (17:21 GMT), today, President Trump was back online, decrying the "Impeachment Witch Hunt"

Yovanovitch details her work in Ukraine.

"From August 2016 until may 2019 I served as the US ambassador to Ukraine. During my tenure...I went to the front line approximately 10 times during a hot war to show the American flag, to hear what was going on, sometimes literally as we heard the impact of artillery and to see how our assistance dollars were being put to use."

"The history is not written yet but Ukraine could move out of Russia's orbit. and now, Ukraine is a battleground," she adds.

"Supporting Ukraine is the right thing to do. it's also the smart thing to do."

Image source, SAUL LOEB/AFP via Getty Images

She says she visited the front in Eastern Ukraine, where soldiers are fighting pro-Russian rebels.

"A secure democratic and free Ukraine serves not only the Ukrainian people, but the American people as well," she says.

She is describing the "potential" the US sees in a democratic Ukraine, and says Russia only sees "risk".

Image source, NICHOLAS KAMM/AFP via Getty Images

"Like my colleagues I entered the foreign service understanding that my job was to implement the foreign policy interests of this nation as defined by the president and Congress," she begins.

"I had no agenda other than to pursue our stated policy goal," she said.

She is now going over her 33-year career as a US foreign policy official.

"I'm grateful the president has released the call record," Schiff says.

"I would now ask the president to release the thousands of other records that he has instructed the state department not to release including Ambassador Taylor's notes, cable, including George Kent's memo, including documents from the office of management and budget about why military aid was withheld."

The New York Times has pointed out that a line about rooting out corruption is missing from the transcript of the April call just released by the White House, but had been included in the original readout.

As Republican Jim Jordan attempts to make a point of order, Democratic committee chairman Adam Schiff keeps telling him to "suspend" his arguments.

"The gentlemen is not recognised," Schiff says several times.

"Holy cow," Jordan exclaims. "Geez!"

Schiff then banged his gavel repeatedly.

Image source, ANDREW CABALLERO-REYNOLDS/AFP via Getty Images

Image source, Alexander Tamargo/Getty Images for Venue Magazine

"When I owned Miss Universe they always had great people. Ukraine was always very well represented," Trump told Zelensky during his first call to the new Ukrainian president.

Zelensky vows to practice his English when he meets Trump.

"All that's beautiful to hear! That's really good. I could not do that in your language," Trump continues.

Nunes in his opening statement again brought up the claim that Democrats were calling on Russian pranksters to get nude photos of Trump in 2016. What's that all about?

The BBC's Paul Wood examined some of the "compromising" claims against Trump in 2017.