What to know about Wednesday's impeachment hearing

• Gordon Sondland, the U.S. ambassador to the European Union, will testify before the House Intelligence Committee as part of the impeachment inquiry on Wednesday morning, starting at 9 a.m.
• Sondland was instrumental in carrying out the pressure campaign to get Ukraine to open investigations to benefit President Trump politically.
• Read and watch highlights of the Tuesday's hearings here and here.
• Download the free CBS News app to stream live coverage of all the impeachment hearings.

Washington -- In the most high-stakes testimony in the impeachment inquiry yet, the House will hear testimony from the U.S. diplomat who discussed efforts to pressure Ukraine directly with President Trump.

Gordon Sondland, the U.S. ambassador to the EU, will appear before the House Intelligence Committee Wednesday morning to explain his shifting testimony, as well as conversations he had with the president about the campaign to get Ukraine to open investigations into the 2016 and a company that had employed former Vice President Joe Biden's son.

Sondland, a major Trump donor, initially told the committees conducting the impeachment probe that he was not aware that a delay in military aid to Ukraine was connected to their willingness to announce the investigations. But in revised testimony earlier this month, Sondland recalled telling a high-level Ukrainian official that the aid "likely" wouldn't be released until an announcement was made.

A U.S. embassy staffer in Kiev testified behind closed doors last week that he had overheard Sondland speaking to the president on the phone on July 26, the day after Mr. Trump's call with Volodymyr Zelensky, the president of Ukraine. The staffer, David Holmes, said he could clearly hear Sondland and Mr. Trump discussing "investigations," with Sondland assuring the president that Zelensky would follow through.

Sondland's hearing is the first of two on Wednesday, with officials from the Pentagon and State Department testifying in the afternoon.

Who is Gordon Sondland?

6:30 a.m.: Sondland is the U.S. ambassador to the European Union, a role he has held since his confirmation in June 2018. Prior to becoming ambassador, Sondland had a long career as a successful hotel magnate and banker. He was also a major donor to the Trump campaign in 2016 and Mr. Trump's inaugural committee, to which he contributed $1 million.

In a shocking reversal earlier this month, Sondland revised his original closed-door testimony because he said reading other witnesses' accounts "refreshed my recollection about conversations involving the suspension of U.S. aid."

Sondland said he now remembers telling a top Ukrainian official that the release of delayed military aid was "likely" dependent on the foreign country announcing investigations that would benefit Mr. Trump politically.

What happened at Tuesday's second hearing

5:45 a.m.: At the afternoon hearing on Tuesday, the former special envoy to Ukraine told lawmakers he was unaware that efforts to pressure the Ukrainian government to opening anti-corruption investigations were targeting the Bidens, but said he would have raised objections if he knew then what he knows now.

Kurt Volker, the former special representative, and Tim Morrison, a former National Security Council official, testified about their knowledge of the events at the center of the impeachment inquiry.

"In hindsight, I now understand that others saw the idea of investigating possible corruption involving the Ukrainian company Burisma as equivalent to investigating former Vice President Biden," Volker said, referring to the energy company that had employed Hunter Biden. "I saw them as very different -- the former being appropriate and unremarkable, the latter being unacceptable. In retrospect, I should have seen that connection differently, and had I done so, I would have raised my own objections."

Read more here.

What happened in Tuesday's first hearing

At Tuesday's first session, two top White House aides told the House Intelligence Committee they found the president's July 25 phone call with the president of Ukraine "improper" and "unusual."

Lieutenant Colonel Alexander Vindman, a National Security Council expert on Ukraine, and Jennifer Williams, an adviser on Russia and Europe to Vice President Mike Pence, both listened in on the call with Volodymyr Zelensky, the president of Ukraine.

In the first of two hearings in the impeachment probe on Tuesday, Williams said she found the call "unusual" because "it involved discussion of what appeared to be a domestic political matter." Vindman said he reported his concerns to his superiors "out of a sense of duty."

Read more here.

How to watch Wednesday's impeachment hearings

• Date: Wednesday, November 20, 2019
• Time: 9 a.m. ET
• Who: Gordon Sondland, Laura Cooper, David Hale
• Online stream: CBSN, in the player above and on your mobile or streaming device
• On TV: Your local CBS station