But Cruz's surge began before that. If Carson's fall was the booster rocket that moved Cruz into second, it appears to have been Cruz's memorable outburst during the (much-reviled) third Republican debate on CNBC that got him off the launchpad.
Here's the Real Clear Politics national polling average since Aug. 1, after Trump was already in the lead. We have marked the CNBC debate and the Paris attacks on the chart so you can see how Cruz's position changed relative to them. Since the beginning of November, he has been on a remarkably consistent upward trajectory.
(Marco Rubio also had a strong debate that time, as he usually does.)
It's important to point out that these numbers are based on public polls, which necessarily trail the events by a few days. But while Cruz polled at 10, 9 and 4 percent in the three polls leading up to the debate, he polled at 10, 13, 8 and 11 percent in polls overlapping with or immediately after it.
If you look at the percentage change in the polling average on a week-by-week basis, Cruz's poll numbers soared during the period between the debate and the attacks — and the change has been positive relative to the prior week on almost every day since. Compare that with Trump, who sagged in the wake of the debate, and Carson, who vanished.
If the attacks in Paris hadn't happened, it's hard to know where Carson and Cruz would be at this point. But Cruz was clearly positioned decently to take advantage of Carson's fall thanks to the strength of his performance in that third debate.