Could the president and/or supreme court block congress actions

Of course he can. If a president has a doubt about the constitutionality of a piece of legislation, he can order his official to go to courts and file a case. In the ultimate end, the US Supreme Court will rule on the case.

Explanation:

The President could choose to veto Congress' bill and publicly state that the reason it is doing so is due to the violation of the Constitution.

Explanation:Supreme Court: If a lawsuit was filed about the law if it passed, the Supreme Court could review it and decide it was unconstitutional.

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explanation:

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