Laura Cooper, a deputy assistant defense secretary, and David Hale, the undersecretary of state for political affairs, will testify before the House Intelligence Committee starting at 5:30 pm ET.
The hearing was originally scheduled for 2:30 pm ET, but the morning hearing with Gordon Sondland, the US ambassador to the EU, went significantly over time.
In his testimony, Sondland said that President Donald Trump, through lawyer Rudy Giuliani, explicitly ordered a specific "quid pro quo" deal with Ukraine to get the country to investigate Joe Biden and the 2016 US election in exchange for public support from the United States. Sondland also said he came to believe that US military aid to Ukraine was tied to that investigation request as well.
At the heart of the inquiry are allegations that Trump and his associates were withholding long-standing American military aid to Ukraine unless the country's new presidential administration agreed to investigate Joe Biden, his family, and a false conspiracy theory about the 2016 election.