Tim Morrison to be first political appointee from White House to testify before impeachment investigators; president has ordered staffers not to cooperate with probe

Some Trump allies looked to discredit decorated officer Alexander Vindman, a Jewish Soviet immigrant, questioning his loyalties as he was born in the region

Lt. Col. Alexander Vindman, who was on the call when Trump demanded Ukraine's president investigate political rival Joe Biden, says he 'did not think it was proper'

Charles Kupperman explains he is waiting for 'judicial clarity' on whether he should obey Congress or the president

US president and allies have largely ignored details of Ukraine probe and instead attacked the investigation process, despite mounting evidence of wrongdoing

Igor Fruman and Lev Parnas allegedly conspired to use foreign money to buy political influence

Democrats say move compromises national security after some bring electronic devices into interview with defense official; hearing delayed 5 hours until officials give all clear

Taylor gives new account of quid pro quo central to impeachment probe, describing Trump's demand that 'everything' Zelenskiy wanted hinged on public vow to investigate Democrats

In four weeks since House launched inquiry into president, he has taken steps in various fields repeatedly testing loyalty of his stalwart Republican allies

Former aide to fired US national security adviser said to tell lawmakers Trump's lawyer 'is going to blow everyone up' with his drive for dirt on Biden