There is a sentense:
Erdoğan reiterated a promise to continue a policy of repatriating Syrian refugees after riding a wave of hardline nationalist sentiment that saw the former ultranationalist presidential candidate Sinan Oğan joined him to declare victory in Ankara.
I copied this from the The Guardian.
I feel it is weird as there is after verbing ... that saw ... . Who saw?
As someone state that the that clause refers to a wave of, so if we make that refers to sentiment, how should we write this sentence. From these, I can tell under what conditions, what that refers to.