My father was born in Italy in 1926 and 1) came to the USA as a minor then 2) was naturalized as a minor when my Italian grandparents obtained US citizenship.
Can I obtain Italian citizenship through my grandfather?
You don't have Italian citizenship, because your father automatically lost his Italian citizenship upon naturalizing in the US when his parents naturalized. Therefore, he had no Italian citizenship when you were born, and could not pass it onto you.
There are lots of guides on the Internet about this topic. I will show a few:
For some more information, you can look at this guide from the Italian consulate in SF. On page 4 is the chart for someone born in the US. If you follow it, Were you born after January 1, 1948? -> Yes/No -> Was your father an Italian citizen at the time of your birth? (The next page has further explanations on how to answer this question. None of the "Yes" situations apply, including "Your father was born in Italy and he did not become naturalized as an American citizen before your birth.", which doesn't apply to you.) -> No -> ACQUISITION (i.e. you don't have Italian citizenship).
Or you can follow the chart for your father (on page 3). Were you born after January 1, 1948? -> No -> Was your father an Italian citizen at the time of your birth? -> Yes -> Did you become naturalized as an American citizen? -> Yes -> Before 1992? -> Yes -> REAQUISITION (i.e. your father doesn't have Italian citizenship).
Here are some more sources if you want:
Q. My Italian-born ascendant naturalized along with his or her minor children. Does that count as renouncing their Italian citizenship if they were minors? A. If your ancestor was naturalized as a minor, he or she effectively renounced his or her right to Italian citizenship. This means that your ancestor was unable to pass Italian citizenship jure sanguinis to his or her children as an adult. Unfortunately, no exceptions are made in these cases.
If you were born in the United States, you may be eligible for Italian citizenship if any of the following situations pertains to you:
A. Your father was an Italian citizen at the time of your birth* and you have never renounced your Italian citizenship. [...]
*If your father was naturalized before your birth, you are not entitled to Italian citizenship.
Yes, by birth to an Italian parent in line with the principle of jus sanguinis.