We’ve got two ways to look at it, one direct, the other indirect, and neither shows any evidence that the debate harmed Rubio in terms of vote choices.
Directly: 67 percent called “the recent debates” an important factor in their vote. Ten percent of them voted for Rubio. The rest said the debates were not an important factor. Twelve percent of them voted for Rubio.
Two points is not a meaningful difference in the exit poll. Rubio’s support was essentially the same whether people decided before or after the debate, and whether or not they said the debates were important to their vote.
Rubio may have some reason for blaming his fifth-place finish on the debates, rather than some other cause. What we don’t see are data to support it.
Rubio's camp did not immediately comment.