“So, politically, as well as legally, it seems possible that the Ukraine/China/Romania stuff won’t matter.”
Hillary was sunk when Trump tied her to corruption. Crooked Hillary rings a bell?
There is a large number of independent voters sensitive to this topic.
This is an excellent point.
The entire FRONTLINE documentary linked below is worth watching, but go to the segment from 42:28 to 44:00 and see how critical this point was with swing voters -- even while the mainstream media and the more "sophisticated" voters in major cities were so quick to dismiss Trump's fixation on Hillary's corruption as a desperate campaign gimmick.
Trump's Road to the White House
Frank Luntz is often derided here on FR, but his commentary on this point is spot-on.