The supreme court did relative recently a decision on a constitutional challenge in regard to copyright when people argued that the Copyright Term Extension Act was unconstitutional. The general rule that came out of the judgement is that copyright law is constitutional as long as it observes the distinction between expression and idea, which the Supreme Court said is the constitutional guarantee, provided that fair use rights are adequately maintained.

For most people it would seem obvious that a 95 years in additional to the life time of the author is counter productive if the goal is to promote the progress of Science and useful Arts, and the limited time part lose its meaning when it keep getting extended, but that is the situation we are in. The meta interpretation I heard after that decision is that the supreme court do not want challenge Congress on the topic of copyright law.