Obama either just joined for political reasons (which wouldn’t explain 20 years of such dedicated participation) or he believes what he is hearin. I can’t think of any other explanation.
Oh he believes it alright, just check out who his Marxist mentor was when he lived in Hawaii. The mentor was a card carrying member of CPUSA. Obama refered to him numerous times in his first book and credited him for getting him interested in politics at a young age.