Why should one blame a particular state ? You should be aware that near about 45% Bengalis doesn't vote for/support Left. And also Bengali Left leaders were not against the deal, it's Mr. Karat and Mr. Yechuri who were always in a mood to blackmail Dr. Singh. One reason is that when you have parties (Left) and people (Mrs. Sonia) calling the shots from outside, who have "No responsibility, but full authority".
If Dr. Singh has any little bit left in his spine, he should throw away PM's post.