Adam Clarke on Deuteronomy 32:32

For their vine is of the vine of Sodom - The Jews are as wicked and rebellious as the Sodomites; for by the vine the inhabitants of the land are signified; see Isa 5:2, Isa 5:7.

Their grapes - Their actions, are gall and worm-wood-producing nothing but mischief and misery to themselves and others.

Their clusters are bitter - Their united exertions, as well as their individual acts, are sin, and only sin, continually. That by vine is meant the people, and by grapes their moral conduct, is evident from Isa 5:1-7. It is very likely that the grapes produced about the lake Asphaltites, where Sodom and Gomorrah formerly stood, were not only of an acrid, disagreeable taste, but of a deleterious quality; and to this, it is probable, Moses here alludes.