The advisory posted on the Interfax-Ukraine news agency website on July 1 sounded innocuous enough.

On the busy agenda of events planned for Volodymyr Zelensky, the newly elected Ukrainian president making his first visit to Canada, would be a meeting with Kurt Volker, the U.S. special representative to Ukraine.

Zelensky, the comic actor who upended Ukraine politics with a decisive win in the April presidential election, was in Toronto for the multilateral Ukraine Reform Conference. His schedule also included a July 2 meeting with Prime Minister Justin Trudeau and Foreign Minister Chrystia Freeland.

The meeting between Zelensky and Trudeau went ahead. But what became of Zelensky's scheduled meeting with Volker is now in the spotlight, after veteran U.S. diplomat Bill Taylor gave closed-door testimony to a group of U.S. lawmakers on Capitol Hill on Tuesday.

Taylor's testimony came as Democrats in the House of Representatives conduct inquiries into whether President Donald Trump committed any impeachable offences by pressuring Ukraine to dig up dirt that would ultimately harm Democratic presidential candidate Joe Biden.

Taylor, the chargé d'affaires for Ukraine, was the latest official to appear before House committees looking into the Trump administration's dealings with the eastern European country. The questioning began in earnest in early September, after Democrats officially learned of an Aug. 12 whistleblower complaint that raised concern about a July 25 phone call between Trump and Zelensky, among other events.

U.S. diplomat William Taylor testified in the Democrats' impeachment investigation of President Donald Trump earlier this week. (J. Scott Applewhite/The Associated Press)

In the 15-page opening statement Taylor prepared for his Tuesday appearance before lawmakers, the long-time diplomat explained the significance of the meeting in Toronto between Zelensky and Volker. Taylor said Volker "planned to be explicit" in that meeting as to why the Ukraine leader's potential visit to the White House was not yet happening, despite it being broached by the Americans as early as May.

Namely, that Trump wanted Zelensky to commit to investigating the Biden family.

'Get to the bottom of things'

According to Taylor, Volker said he was going to relay to Zelensky in Toronto that Trump wanted co-operation on investigations to "get to the bottom of things." Taylor said it was unclear to him what exactly Trump or Volker meant, and his opening statement doesn't delve into the meeting further.

It's not entirely clear whether Volker followed through on his promise to be "explicit." Taylor's statement jumps ahead to developments beginning in mid-July, and reporting of details from Tuesday's closed session didn't offer any further details around what might have happened in Toronto.

Ukrainian President Zelensky campaigned on a promise to root out corruption in his country. (Valentyn Ogirenko/Reuters)

Volker himself appeared before the House committees on Oct. 4, and his opening statement does mention meeting the Ukraine president in Toronto. To the extent he discusses it, Volker casts it as cautioning Zelensky in a private discussion that Trump's personal attorney, Rudy Giuliani, was likely negatively influencing the U.S. president when it came to Ukraine policy.

"I made it clear that [Giuliani] does not speak for the U.S. government, but is a private citizen and the president's personal attorney," said Volker, who resigned from his post before appearing before lawmakers.

Based on reporting, Trump's own statements and a partial readout of the July 25 call provided by the White House, getting to "the bottom of things" appears to have had two main components.

Trump wanted Zelensky to have officials in Ukraine investigate 2020 presidential candidate Biden and his son, Hunter — who had served on the board of Ukraine-based energy giant Burisma for over two years while his father was U.S. vice-president — for potential corruption.

While many have questioned the wisdom of Hunter Biden taking on the role in Ukraine, no credible allegations of illegality have emerged concerning the Bidens.

The president also expressed hope Zelensky's administration would pursue a theory, often posited in right-wing media outlets, that a Democratic committee server breach ahead of the 2016 U.S. election emanated from Ukraine. A host of investigations, both in Congress and in special counsel Robert Mueller's probe, have traced the cyber-intrusions to Russia.

'Irregular channel'

According to his opening statement, Taylor told lawmakers that he realized, after arriving in Kyiv, that in addition to the normal diplomatic processes run through the State Department, there was an "irregular channel" for Ukraine. It consisted of Volker, ambassador to the European Union Gordon Sondland, Secretary of Energy Rick Perry and Giuliani, who is not a State Department or national security official.

Congressionally approved U.S. security assistance to Ukraine worth around $400 million US was delayed for several weeks and only released on Sept. 11, two days after the House intelligence committee was notified of the whistleblower complaint.

Kurt Volker, U.S. Special Representative for Ukraine Negotiations, had a meeting booked with the Ukrainian president in Toronto on July 1. (EPA-EFE)

Taylor's unease with what he was seeing unfold in Ukraine was public before his appearance on Capitol Hill. Among texts and documents released by Democrats in early October, Taylor told Sondland on Sept. 9, "I think it's crazy to withhold security assistance for help with a political campaign."

Trump has insisted there was no quid pro quo attached to his request to Ukraine regarding the potential probes. The U.S. president has also said his interest regarding the Bidens is not personal, but part of a commitment to root out corruption.

The president was also unimpressed with what he heard about Taylor's session on Capitol Hill, branding him a "Never Trumper" on Twitter.

A host of Taylor's former colleagues have attested publicly in media reports in recent weeks that Taylor was apolitical, and his career includes three decades of work serving in both Republican and Democratic administrations.

Taylor, who had served as ambassador to Ukraine during the George W. Bush administration, replaced Marie (Masha) Yovanovitch, the U.S. ambassador to Ukraine who was ousted abruptly in the spring.

A number of Trump loyalists disrupted for a time Wednesday's deposition with Laura Cooper, assistant secretary of defence. The Republicans have been angered by the closed-door nature of the hearings, but Democrats have said public testimony will come in the near future.

The hearings will continue with a Saturday session featuring testimony from Philip Reeker, acting assistant secretary for European and Eurasian Affairs.