Yes, both the President and the Supreme Court can play a role in blocking actions taken by Congress that are unconstitutional.
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The Supreme Court: The primary role of the Supreme Court in this context is judicial review, the power to interpret the Constitution and assess the constitutionality of laws passed by Congress. If Congress enacts a law that violates the Constitution, individuals or entities affected by that law can challenge its constitutionality in court. If the case reaches the Supreme Court, the justices can declare the law unconstitutional and effectively block its enforcement.
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The President: The President has the power to veto legislation passed by Congress. If the President believes that a proposed law is unconstitutional, they can use the veto power to block it from becoming law. However, Congress can override a presidential veto with a two-thirds majority in both houses, which means this power is not absolute. Additionally, the President can influence constitutional matters through executive orders, which must still comply with the Constitution and current laws.
In summary, the Supreme Court can invalidate unconstitutional laws via judicial review, while the President can veto legislation they believe is unconstitutional, although this can be overridden by Congress.