Alexander Vindman, Kurt Volker, Tim Morrison, and Jennifer Williams are testifying in Tuesday's impeachment hearings. Here's how to watch.

Lt. Col. Alexander Vindman, top Ukraine expert on National Security Council; Jennifer Williams, foreign service aide detailed to Vice President Mike Pence; Tim Morrison, NSC's former official in charge of overseeing Russia and Europe policy; Kurt Volker, the US's former Special Representative to Ukraine.
Vindman and Williams directly listened in on the July 25 phone call at the center of the impeachment inquiry.
Volker and Morrison will give testimony showing how the phone call was just one data point in President Donald Trump's months-long campaign to strongarm Ukraine into delivering political dirt while holding up military aid and a White House meeting.
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This week's impeachment hearings will kick off on Tuesday with four current and former administration officials scheduled to testify in open session.

Here's who's testifying:

Lt. Col. Alexander Vindman, the top Ukraine expert on the National Security Council.
Jennifer Williams, a foreign service aide detailed to Vice President Mike Pence.
Tim Morrison, the NSC's former official in charge of overseeing Russia and Europe policy.
Kurt Volker, the US's former Special Representative to Ukraine.

Vindman and Williams will testify together beginning at 9 a.m. ET before the House Intelligence Committee. Morrison and Volker will jointly testify in a second hearing beginning at 2:30 p.m. ET.

The hearings will be broadcast live on C-SPAN and all the major cable news networks. They will also be streamed on YouTube, and Insider will embed a livestream of both hearings here when they begin.

Both Williams and Vindman directly listened in on the July 25 call between President Donald Trump and Ukrainian President Volodymyr Zelensky that's at the center of the impeachment inquiry.

Vindman also witnessed efforts by John Eisenberg, the NSC's chief lawyer, to bury records of the call after several officials sounded the alarm over what Trump had said.

During the phone call, Trump repeatedly pressured Zelensky to investigate former Vice President Joe Biden and his son for corruption. He also asked Zelensky to look into a bogus conspiracy theory suggesting it was Ukraine, not Russia, that interfered in the 2016 election and that it did so to benefit Hillary Clinton's campaign.

Volker and Morrison will give testimony showing how the phone call was just one data point in a months-long shadow foreign policy campaign to strongarm Ukraine into delivering Trump the political dirt he wanted. While doing so, the president withheld a $391 million vital military aid package to Ukraine as well as a White House meeting for Zelensky.

Three officials are scheduled to testify on Wednesday: Gordon Sondland, the US's ambassador to the European Union; Laura Cooper, a deputy assistant secretary at the State Department; and David Hale, the undersecretary of state for political affairs at the State Department.

The last hearing this week will take place on Thursday morning, with just one official scheduled to appear: Fiona Hill, the NSC's former senior director for Russian and Eurasian affairs.