@oristarA,
oristarA wrote:
Context:
For all the sympathy Pollard generated in Israel, he was a hard case to push in America; he had sold our country’s secrets for money, not conviction, and for years had not shown any remorse.
Yes, hawkeye is right. In this case, we could also say he was a "hard sell" to the American public. It would be hard to make Americans like or accept him.
In the other sentence, it seems like this guy was talking about his composition instructor. She was very good, but he wasn't a good student, so his writing doesn't reflect how good his teacher was. His failure to learn made him a hard case. It was hard for the teacher to accomplish her goal of teaching him to write well.