For now, it comes down to this: the US State Department is at war with the White House. State's allies in the Democratic majority congress want to help overthrow the occupant of the White House because he's interfering in the department's foreign policy. The lifers at State are the same ones who executed a coup in 2014 against Ukraine's government and threw out the elected president Victor Yanukovych because he tilted to join a Russian-backed regional customs union rather than NATO. State's diplomatic lifers are old hands at coups. Now they're at it at home, right here in the USA.
Ever since the Maidan Revolution of 2014, they have worked sedulously to exert control over Ukrainian affairs. And they especially can't stand that the recently elected president Zelensky declared that he wants to improve his country's relationship with next-door-neighbor (and ex-sovereign) Russia. The occupant of the White House, Mr. Trump, had often expressed a similar interest to improve the USA's relations with Russia. State would prefer to amp up a new cold war. Mr. Trump has some nerve interfering with that!