Former FBI Director Jim Comey, or his ghost writers, seems to have a talent for clearly stating situations. I liked this one, from his recent opinion piece in WaPo:
The president’s oath has always been slightly different. Because the holder of that office has unique responsibilities to the rule of law, the Constitution spelled out the exact words for that job. The president must promise not just to protect and defend the Constitution, but also to “faithfully execute the office of president of the United States.” And there is the problem for Trump, and every senator and representative.
If Congress passes a law giving a vulnerable ally hundreds of millions of dollars in military aid desperately needed to fend off a relentless Russia, and the president of the United States uses that money to coerce the desperate ally to provide electoral dirt on his likely opponent, is the president faithfully executing his office? And if the president conditions White House meetings on acquiring the same foreign dirt to help him get reelected? The answers are obvious.
Connecting the requirements incumbent on both the President and the Senators with a clear statement of the apparent facts of the Ukrainian matter, it makes it clear that, if the facts are as the Democrats claim they are, then the Senators, if they wish to retain their moral integrity, must vote for conviction.
Which leaves it up to the Democrats to make the case forcefully.