It was the US who desperately initiated the whole thing (because they are trending down). CN is happy with the way things are (because they are trending up). So all the pressure was on the US to alter the trend, and they failed.
In summary; they tried to tell CN what to do, and CN politely said “no, we will keep doing things our way, at our pace.” Bluff called, Trump must give up on this for 2020 to get re-elected (requires a saving face fake deal which gets farm purchases back up for key voters).
CN only needs to keep running out the clock, as the US socioeconomically collapses. Win thru non-action; the way of the sage.