Updated at 5:21 p.m. ET
A State Department staffer overheard President Trump asking a top diplomat about "investigations" he wanted Ukraine to pursue that he believed might help him in the 2020 election, another senior diplomat told Congress.
That staffer is expected to tell his story directly to House investigators at a closed-door deposition on Friday.
The new subplot about the overheard phone conversation was one of a small number of new details to emerge from Democrats' first open hearing in their impeachment inquiry into Trump on Wednesday.