Final answer:
The Supreme Court can declare presidential actions unconstitutional as part of its checks on the executive branch, but it depends on the president and the executive branch to implement and enforce its rulings, a process known as judicial implementation.
Step-by-step explanation:
If the Supreme Court feels the president has not followed the law, it has the power to declare actions by the executive branch unconstitutional. This is part of the system of checks and balances that the judiciary has over the other branches of government. The Supreme Court hears cases involving federal law and serves as the nation's final court of appeal. While the Court has the authority to make such rulings, it relies on the executive branch to implement or enforce its decisions. This reliance sometimes results in tension, as historical instances show with presidents like Andrew Jackson or Abraham Lincoln who chose to ignore the Court's decisions.
Judges are expected to follow the Constitution and the law despite their own policy preferences. For instance, Supreme Court Justice John Paul Stevens expressed regret over some majority opinions due to the need to uphold federal statutes, showing the necessity of abiding by the law.
The judiciary also finds its decisions effective only when they are heeded by the other branches. This process is called judicial implementation. Despite its significant influence in policymaking, the judiciary has no direct means to enforce its rulings and depends on the executive for implementation.