Nominalize
Nominalize , transitive verb
(Grammar, Linguistics) To convert into a noun; as, a nominalized sentence; a nominalized adjective or verb.
In a sentence of the form:
“That Kennedy would have been a great president if he had not been assassinated is one of the enduring myths of the Camelot conceit.”
the sentence “Kennedy would have been a great president if he had not been assassinated” has been nominalized by the introductory “that”.