。
I think he's a fool.
Literal
I [topic-は] he [topic-は] fool [is-だ] [quotative-と] think.
Interesting: two は in the same sentence. Normally avoided, but here the outer は topicalizes the speaker while the inner は sits inside the embedded clause topicalizing 'he' as a contrastive topic within the opinion. Usually the embedded subject would take が; the は form gives slight emphasis or contrastive foregrounding.