Impeachment Primer: Who will testify and what they're expected to say

After weeks of closed-door depositions, the impeachment inquiry into allegations of abuse of power by U.S. President Donald Trump is set totake the spotlight with public hearings.

In full view of the American people and the world, the televised hearings by the House of Representatives select committee on intelligence begin Wednesday, with a second hearing scheduled on Friday.

The hearings will go a long way to helping the public understand the allegations that the president abused the power of his office for personal political gain by pressuring Ukrainian President Volodymyr Zelensky to investigate former U.S. vice-president Joe Biden and his son Hunter around the latter's business dealings in Ukraine.

Here's a guide to who is testifying, what they'll be asked aboutand why it matters.

What will happen

Wednesday's hearing begins at 10 a.m. ET,with live coverage onCBCNews.ca, CBC News Network and the CBC News YouTube and Twitterpages.

Unlike at previous hearings, such as those relating to the final report of the special counselRobert Mueller,lawyers, not committee members, will dothe bulk of the questioning.

Democratic and Republican lawyers will each get up to 45 minutes to question the witnesses. Committee members from both parties will then have their chance, but with just five minutes available to them.

Who willtestify

William B. Taylor, charg d'affaires,perhaps the highest profile witness listed, was America's top envoy to Ukraine, taking the role after former U.S. ambassador Marie Yovanovitch was ousted in May.

He was asked to take the job by Secretary of State Mike Pompeo, which, Democrats argue, adds to his credibility. He was ambassador to Ukraine from 2006 to 2009.

George Kent, deputy assistant secretary for European and Eurasian affairs,is a career foreign service officer with more than 27 years of experience. He has servedunder five presidents, three Republicans and two Democrats. He testified behind closed doors under subpoena, in defiance of the State Department which tried to block his testimony.

What Taylor will say

Taylor's testimony in the closed sessions has been considered among the most damaging tothe president.

It gets to the heart of an allegation of a quid pro quo alleging thatTrump ordered that vital military funding and the promise of a meeting withZelensky be withheld unless Zelensky announced an investigation into the Bidens.Joe Biden was vice-president forover two years whenHunter served on the board of directors of Burisma, a Ukrainian gas company.

"That was my clear understanding, security assistance money would not come until the president [of Ukraine]committed to pursue the investigation," Taylor said, according to the deposition transcript.

Taylor also told investigators that the push for the announcement of a Ukrainian investigation which would benefit Trump, who sees Joe Biden as a top rival in the 2020 presidential race was spearheaded by Trump's personal lawyer Rudy Giuliani.

Giuliani was part of a second track of diplomacy, Taylor testified, that worked parallel to career officials, and pushed the president's personal interests over the country's foreign policy goals.

"I had been making, and continue to make, this point to all of my Ukrainian official contacts. But the push to make President Zelensky publicly commit to investigations of Burisma and alleged interference in the 2016 elections showed how the official foreign policy of the United States was undercut by the irregular efforts led by Mr. Giuliani," Taylor told lawmakers.

What Kent will say

Kentis expected to corroborate much of the information provided by Taylor and others. His testimony provided a clear indication that the direction to squeeze Ukraine came directly from Trump.

Summarizing a conversation between U.S. Ambassador to the EUGordon Sondland and Trump, Kent testified "POTUS wanted nothing less President Zelensky to go to [a]microphone and say investigations, Biden, [Hillary] Clinton."

Kent has also provided testimony about Giuliani's efforts on behalf of Trump, to force out Yovanovitch, the former ambassador to Ukraine. Kent said the effort to smear Yovanovitch was part of a "campaign of lies" by Giuliani.

Yovanovitch, scheduled totestifyon Friday, says she was ousted because of her anti-corruption work in Ukraine.

The Democrats' strategy

The Democrats, led by House intelligence committee chair Adam Schiff, want to show that the president used the State Department and other sections of the bureaucracy to advance his personal political goals and undermine U.S. foreign policy.

They're hoping testimony from Taylor, a non-partisanchosen by the Trump administration to work on the Ukraine file, will help bolster their case.

As well, Kent can cover a lot of ground, from the question of influence from the White House, to efforts by the State Department to block testimony and co-operation, which could end up as an article of impeachment for obstructing the investigation.

The Republicans' strategy

In advance of the hearing, the Republicans released a memo outlining four key areas they want to focus on in their defence of the president. Their key point:the July 25call shows "no conditionality or evidence of pressure," something both Trump and Zelenskyhave publicly stated.

The Republicans also argue that Trump was deeply concerned about corruption in Ukraine, not just about the actions of his political rival. They note thatthere couldn't have been a quid pro quo becauseUkrainian officials didn't know the aid was put on hold (although the New York Times reported last month that they did learn about it in early August).

That aid, Republicans say, was eventually released and Trump did meet with Zelensky in September, with no investigation of the Bidens having taken place.

A witness listsubmitted over the weekend by the Republicans included Hunter Biden, a sign they might want to focus on his actionsmore than Trump's. Democrats are expected to reject those requests.

During questioning of the witnesses, look for Republican members of Congress to point out thatTaylor and Kent never spoke to Trump directly, meaningtheir information is second- or third-hand. They might push a line of questioningthat shows the events under investigation were not directly influenced or ordered by the president.

Republicans might also hammer the message thatwhat took place between the Trump administration and Ukraine, while distasteful, doesn't rise to the level of"high crimes and misdemeanours," theconstitutional standard for impeachment.

The big picture

With the Democrats holding a majority in the House, many observers believe impeachment is a foregone conclusion.If so, the next step would be a trial in the Senate.

So the challenge is whether the evidence revealed in public hearings is enough to sway public opinion and convince enough Republican senators to vote to remove the president. About 20 would need to cross the aisle to give the two-thirds majority required.

What's next

Yovanovitch will testify on Friday. She will detail how she believes Giuliani and Trump pushed her out to clear a path for their plans in Ukraine.

More hearings are scheduled next week with eight new witnesses scheduled to testify. On Tuesday morning, the committee will hear from Jennifer Williams an aide to Vice President Mike Pence, who listened in to the July 25 call.

The key witness that day will beLt.-Col. Alexander Vindman, who listened to the call between Trump and Zelensky and immediately raised red flags. He's also linked Trump's chief of staff Mick Mulvaney to efforts to coerce Ukraine into a politically motivated investigation.

On Tuesday afternoon,Kurt Volkerformer special envoy to Ukraine and Tim Morrison from the National Security Council will testify. Volkerprovided text messages about officials concerns regarding aid to Ukraine. He testified that he didn't know about efforts to investigate the Bidens but warned Ukraine about Giuliani's influence in U.S. policy.

On Wednesday, U.S. Ambassador to the E.U. Gordon Sondland will testify. He's been linked directly to efforts to pressure Ukraine to announce an investigation into the Bidens, even changing his testimony to reflect that.

OnWednesday afternoon, David Hale, the third highest ranking official at the State Department and Laura Cooper, a Defense Department official will sit before the committee. Democrats say Cooper will showhow Trump froze Congressionally-approved aid to Ukraine and raised concerns about the hold.

Thursday sees Fiona Hill, former White House Russia specialist testify. She told officials about a July meeting in which Sondlanddiscussed exchanging aid for investigations. She also discussed deep concerns held by National Security Advisor John Bolton about Trump's policy towards Ukraine.