Erin Burnett Outfront

Former Trump adviser testifying in impeachment probe; State department official, ambassador set to testify this week; Washington Post: Trump's EU Ambassador plans to tell lawmakers Ukraine quid pro quo denial was dictated by Trump; Former Trump adviser still testifying in impeachment probe; Federal investigators talking to witnesses about Giuliani's Ukraine work since at least August; New Poll: Majority of GOP voters say it's ok for U.S. President to ask for U.S. President to ask foreign leaders to probe political rivals; Biden takes aim at Trump; vows his kids will not have White House office; New poll shows Biden, Warren locked in close race as Biden takes on Trump over ethics; Warren and Biden had Democrats on eve of CNN debate; Sanders to appear on CNN debate stage tomorrow night; will be his first campaign event since his heart attack; Sanders back in action at CNN debate tomorrow night; Sanders: Warren says she is a capitalist, I am not; After sparring on gun control, Buttigieg slams O&#