The President of the United States has specific powers when it comes to legislation. He or she can veto a bill, which means rejecting it, or sign it into law, thereby approving it. However, the power to determine whether a law is constitutional or unconstitutional lies with the judicial branch, particularly the Supreme Court. This separation of powers is a fundamental principle of the U.S. government, ensuring that no single branch has ultimate authority over the others. Therefore, the correct answer is that the President cannot rule a bill as constitutional.