LOL! Looks like Cruz has peaked in RCP avg.
It would be interesting to review the daily events and/or Trump statements of the day for each step up on that chart. Also, I cannot remember the exact date of the Paris and San Bernardino attacks but I suspect it was around the time that the Ben Carson line starts to drop.
This is why you have to look at the underlying numbers and not just the Trend line. The only reason Trump went up and Cruz went down in the Trend line is because one of the polls that rolled off the average was one that showed Cruz up by 2 over Trump. Now that poll was obviously an outlier and had skewed the trend against Trump - but then you had the CNN poll showing Trump up by 33 points, which was also an outlier in the other direction, so they tended to balance each other out, but now you just have the CNN poll in the average, skewing the trend to the high side for Trump.
This poll today is the only national poll taken since the last 2 debates. It shows Trump losing significant ground since the last ABC/WaPo poll, which had Trump with a 16 point lead. Whether other national polls will show a similar trend is unknown at this time, but the poll does seem to reflect what we observed on Saturday.