That is a stretch. Although the article does not cite any source for the 8O% claim. The Gallop organization has data that shows support for the Israeli side has varied from 10% to 50% over the last 30 years. Today, a large majority of American's don't want us to take sides in the conflict.
One would never guess that, reading just what is posted here.
Obviously I cant speak for the author. However recent polls Ive seen seem to be in the area of 50% supporting Israel, 10%-12% the Palistinians, with a big chunk of undecided. My guess is hes referring to 80% of those who expressed an opinion.