By ABC News
It's one of the rarest political events in American history, one that only three presidents have ever experienced before today. Just months after the release of Special Counsel Robert Mueller's report, the White House finds itself under fire from a new front: an impeachment inquiry. Who was on that July 25th call between President Trump and President Zelensky? What was promised and who was pressured? And how has that one phone call raised the question, once again, of possible foreign intervention in U.S. elections and "quid pro quo" demands to other foreign leaders? We'll bring you all of our exclusive reporting -- from the halls of Capitol Hill to Maiden Square in Kyiv. Along the way, you'll get insight from legal analysts and historians, politicians and principals -- those who are driving the developments in this rapidly-unfolding story -- all as we count down the days until an impeachment vote and a possible senate trial.